And what is the duck duck goose thing? I doubt Cersei will think Arianne as more beautiful that her. Cersei is drop dead gorgeous (even if she has stretched marks on her belly), while Arianne … is very short, a bit round (I don’t say round people can’t be beautiful I am just in Cersei’s mind here), and description of her … she isn’t so much praised to be beautiful as Dany, Cersei or even Sansa are.

Duck, Duck, Goose is my way of joking about the whole “threefold revelation" thing. Cersei is still a good looking woman, but youth is no longer on her side, and she’s drinking and eating heavily which will take its toll.

Everything I’ve ever read about Arianne says she’s incredibly beautiful. She’s not Twiggy, but according to Ser Mix-A-Lot, the Lion-el of Richie, and lady Meghan of House Trainor, her body type is much to be admired. 

I am actually interested by your theory about how the Dance will happen. Do you think Aegon will “steal” a dragon? How? How will Dany arrive in Westeros? What about Euron/Daario + Victarion plot? Will Daenerys have to kill one of her dragons of “they join” her enemy? How will she understand that Aegon is false?

The stealing of the dragons I don’t think is going to work long-term in either case – I’m pretty sure at this point that Tyrion’s going to ride Viserion, given the bit from his TWOW chapter where he picks up the white cyvasse dragon. Dany’s riding Drogon, natch. And that leaves Jon to ride Rhaegal, named after his father. 

So I’m pretty sure the horn flubs – just like the other magical horn which never brought down the Wall. Moqorro is clearly planning to betray Victarion to his death.

As to how she understands Aegon is false, I think:

  1. Prophecy. She knows both from the HOTU and Qaithe that the “mummer’s dragon” is bad news.
  2. She’s not going to want to accept Aegon’s offer. She’s the prophesied one with the dragons, and she’s not going to accept being second fiddle to Arianne Martell with someone else sitting the Iron Throne.

KL couldn’t be retaken because Aegon would have Margaery amongst others, Tommen taken out or captured  and the seat of political legitimacy. The Tyrells still have an army near KL. I think you’re missing the point, when a rival army was moving to attack KL, he moved to aid KL to the more immediate danger. Also, Euron will likely have been taken out sometime in TWoW.    
Well, GRRM didn’t call it the second Dance of Dragons for nothing. There are bound to be parallels between the two wars, or why give us a detailed description of the Dance? Aegon is trying to form the image of Aegon the Conqueror reborn, I think. Trying to take KL with no navy and a smaller army makes little military sense, especially since there is a Tyrell army of not insignificant size already in the field led by a competent commander. There is also Randyll Tarly to consider who is no pushover. Aegon needs enough military strength to be unrivaled by anyone else in the field.   
Yet, from that description what more could Dany do? Cersei would have already had everything taken from her. I think that is where your argument fails, no offense. Cersei has thicker plot armor than Aegon. 

When a rival army was moving to attack King’s Landing, Tywin moved to save Casterly Rock. It was only when he failed and got word of an alliance in the nick of time that he moved to King’s Landing. 

If Euron is taken out “sometime” that’s not enough time. Garlan is a thousand miles away. And Aegon’s got a 500 mile head start on him. 

He’s already got a parallel – King vs. Queen – he’s not going to literally redo the whole thing. That’s not how GRRM works when it comes to historical analogy – he always remixes. 

As for Aegon – if he gets the Martell army and the Stormlords, he’s got the bigger army. And the Tyrell army isn’t entirely loyal to King Tommen ‘Baratheon’ – remember, these guys all fought for the Targaryens back in the day. And it’s a very good possibility that House Tarly fought for the Blackfyres – their house is right there up against the Red Mountains to defend against the Dornish, a lot of their neighbors fought for the Black Dragon, they have a warrior ethos that would clash with Daeron II’s academic sensibilities, etc. 

Cersei’s plot armor extends no further than not being able to be killed before Jaime shows up again. 

Any chance Aegon could hit Oldtown to repel an Ironborn attack? That is to say, using Stannis’s approach: Winning the realm by saving it, then proceeding to KL; but with Connington sowing a plague all along the way.

Nah. 

1. Saving the realm to win it is meant to distinguish Stannis from the other claiimants. Aegon isn’t a main character, he’s a foil who’s going to die. 

2. Aegon has to be dealt with conclusively and quickly. There’s not time for Dany to have a drawn-out war with Aegon AND save the day when the Others fall AND deal with the stone dragon, etc. 

I don’t think you’re taking into account defense mutlipliers with at least 20,000 men in the Tyrell army inside the walls being able to take on ten times that number, and the numbers you give are around 50,000. Ships could block the passage across the Blackwater. They could hold off Aegon long enough for a relief force to arrive from the Reach or the Westerlands. There is still the problem of another Tyrell army in the field.   
Garlan’s not coming to help? If they lose HG they can retake it, but if KL falls they lose the war. Besides, Redwyne’s fleet has arrived to keep the Ironborn busy. If Tywin Lannister was willing to forgo aiding the Westerlands to save KL then I think Garlan would do the same.
Unless you have copy of TWoW in front of you, I don’t think you can effectively say that Aegon won’t go to Oldtown anymore than I can say he’ll go North (I don’t think he will). The Hightowers are the most powerful vassals of the Tyrells, and as Stannis demonstrated, aiding lords against Ironborn is a good way to win support. The Hightowers are pissed with the government in KL over their lack of response to the Ironborn. Winning them by aiding against Euron when assaults the city would be a massive blow to the Tyrells. If Aegon plans to win Reach lords he may have to go into the Reach, Aegon is going to need every sword he can get to defy the power of both HG and CR. The Hightowers were also the chief supporters of Aegon II in the second Dance.   
The HS crowned Aegon I in Oldtown, and none of the other claimants waited to be crowned in KL except Joffrey. There is precedent for being crowned in Oldtown as mentioned. There is nothing stopping the HS from going to Aegon. 
Except Aegon cast her down in that interpretation when it is supposed to be the younger queen. Whether or not Dany arrives, Cersei will have been dethroned and lost all she holds dear: her kids, her seat and her power. That still begs the question of why the prophecy mentions Dany if it doesn’t fit in any way?
I think we will wait and see in TWoW. If I am right I get exclusive bragging rights, the same goes for you. 

Mace is going to have to take to the field against Aegon – so no defensive multiplier.

You have it backward – if HG falls, the Tyrells fall. KL can be retaken. Look again at your Tywin example. When it came down to it, he chose to march west rather than south, because losing Casterly Rock would have lost him the war. These are feudal armies that exist as long as the lords and knights who make them up choose to follow – once you’re seen as weak, your army crumbles.

Going to Oldtown goes against all military logic, and there’s no reason to do it except for an over-literal replaying of the Dance of the Dragons. Aegon I was crowned in Oldtown, but every King since has been crowned in King’s Landing, because that’s where the Iron Throne is. There’s a reason why both Stannis and Renly went for King’s Landing and not Tywin – because King’s Landing is where political legitimacy comes from. 

It’s going to fit – Cersei won’t have fallen completely yet before Dany arrives to finish the job. 

Regarding the “Younger, more beautiful queen” and the Rule of Three, I think you overlooked Sansa. Cersei definitely viewed Sansa as a threat, which is why she treated her so poorly (we just didn’t have the benefit of Cersei’s POV). Sansa (duck), Maergery (duck) and Arianne (goose). The head-fake may be that Cersei might not perceive Arianne as beautiful, and therefore not a threat.

She did for a while, but then she dismissed her as a suspect. Hence constantly calling Sansa stupid, getting her betrothal broken, etc. 

The Cause of Skagos’s Rebellion

In WOIAF, it is mentioned that King Brandon IX forbade the Skagosi the sea whereas before they described as accustomed to crossing the Bay of Seals to trade with the rest of the North. It was their raiding that led to Brandon forbidding them the sea.   
Do you think the Skagosi rebellion in Daeron II’s reign might have been over regaining the right to have access to the sea, ie build and keep ships, breaking their centuries-long isolation? 

Well, they were accustomed to raiding as much as trading – they didn’t do one then the other, they did them both at thre same time. 

It’s as good a bet as any, and until we get to Davos’ TWOW chapters, we’re not going to know what motivated the Skagosi. 

Aegon’s Crowning

The army he currently has is not enough to take and hold King’s Landing. If he tries, there is still the force along the Mander with Garlan to consider to crush him against the walls of King’s Landing. He needs to gather a large enough force to be able to oppose any other challengers. It is going to take a while to convince everyone he is the real Aegon, and gather enough support. 
Nothing in the vision explicitly says it is King’s Landing, so that isn’t a certifiable fact at the moment. King’s Landing isn’t the only city in the realm, there is also Oldtown. The first Aegon was crowned in Oldtown, and Oldtown supported Aegon II. The High Septon could come to Aegon, and crown him in the Starry Sept, the original seat of the Faith, with Aegon following in the footsteps of his namesake. They are trying to portray Aegon in the image of Aegon I. One doesn’t need to sit the Iron Throne to be king. Aegon the Conqueror was called “king” before the Iron Throne was even forged. To be called “king” one simply needs to be crowned. 
I think in the second Dance, Oldtown will be Aegon’s base while Harrenhal will be Dany’s. 
Also, there is one inconsistency. You say Dany is the younger queen that will cast Cersei down yet Aegon will take King’s Landing from Cersei, or rather cast her down. In that case the younger queen would be Arianne not Dany. So if Dany is the younger queen to cast Cersei down, then that means Aegon won’t take King’s Landing, since by the time Dany arrives Cersei will have already been cast down. 

Aegon has 10,000 men. The Martells have 25,000. Many of the Stormlords have stayed out of the war. And there are friends of the Gold Company in the Tyrells’ ranks. That’s all he needs.

Garlan’s army is a thousand miles away and busy fighting the Ironborn. They’re not coming to help.

Aegon is not going to Oldtown – King’s Landing is the capitol, the Iron Throne is the symbol of a unified monarchy, the High Septon he needs to crown him is in King’s Landing, and it’s less than 500 miles away. He’s not going to go 1400 miles out of his way.

I think Cersei’s going to be awaiting trial at Aegon’s pleasure, thinking Arianne was the queen she didn’t see coming, when Dany arrives. It’s a classic prophecy fake-out, the same way that Tyrion isn’t the valonqar. 

Given their access to water transport routes to underserved parts of the Seven Kingdoms and several of the Free Cities, Saltpans/Maidenpool should be more important trading ports (as should Seaguard at the other end of the Blue Fork). One would also expect a trading port on the eastern side of The Neck—where the Kingsroad passes closest to The Bite seems a likely spot. Is this due to Westerosi feudalism being a poor system to support economic development or is something else going on?

Well, there is a trading port on the eastern side of the Neck, it’s White Harbor. Which has a first mover advantage that would probably put the kibosh on any competitors. 

And yes, Saltpans and Maidenpool should be more important. The story here – as with Duskendale – is the lack of royal charters inhibiting development. In the case of Saltpans and Maidenpool, we learn that there was “a tendency for the kings of the past to refuse the charters that might have given some Saltpans or Lord Harroway’s Town or Fairmarket leave to expand.” (WOAIF, p.151) This is possibly because the Kings of the Rivers and Hills weren’t that secure in their powerbase and wanted to ensure that the more easterly parts of their realm (in the case of Saltpans and LHT and Maidenpool) or the former capital of a previous House (in the case of Fairmarket) didn’t get too powerful and challenge the Kings for supremacy. 

The question is why didn’t this change when the Targaryens came? Well, as with Duskendale, the Targaryens weren’t interested in letting other cities “vie for trade with King’s Landing,” (WOIAF, p. 118) as the Iron Throne gets 100% of the income from King’s Landing trade and would get a smaller cut from any other lord’s port. Given that every city in Westeros predates the Targaryens, I don’t know that there’s any examples of a Targaryen monarch giving a city charter (not a town charter, the two are different) and creating a new city. 

In fact, if you look at Targaryen development policy – most noticeably the royal highways built by Jaehaerys I – the whole point is to route traffic through the capitol. Thus, the River Road abruptly turns south at Lord Harroway’s Town straight to King’s Landing, rather than continuing along the bank of the Trident to Maidenpool; Maidenpool in turn is on the Rosby road, so that you have to travel to King’s Landing before taking your goods anywhere important via roads.

So I think the story here is the weakness of the post-Draconic monarchy driving policy to favor the King’s personal income and thus the capitol. If the Targaryen monarchy was more of a genuine nation-state, you might well see the Kings doing more to promote economic development more widely. 

Play general for a second – you’re Euron Greyjoy. Let’s be generous and say you have 6,000 men divided among rowers and marines, and while your men are blooded, they’re not the from the Iron Fleet, so they’re not the best fighters the Iron Islands has to offer. You control the Shield Islands and the mouth of the Mander. Paxter Redwyne and his 40,000 men are headed your way with larger superior ships. How do you (without any sort of magical deus ex machina) defeat him?

I don’t think I do. I think that’s precisely why Euron’s turned to a magical deus ex machina. Generally speaking, habitual users of powerful hallucinogens aren’t the carefulest of generals.