“Umm…I don’t think that Dany will be thrown out by a revolt by the smallfolk. Rather, I think Cersei will be thrown out by a revolt by the smallfolk, replaced with Aegon, and then Aegon will be overthrown by Daenerys. ”
I don’t think Aegon will take King’s Landing, but Dany will arrive to start the second Dance before he gets the chance in a kind of parallel to Stannis and Renly in that the one with support of the Red Faith and proclaimed AAR on Dragonstone sends out ravens saying boy king isn’t who he says he is while the popular one has a large army made up of Reach men and stormlanders). I think rather GRRM is building up Cersei’s fall towards the end. 

Here’s why I don’t think that works. At least the way I interpret the House of the Undying Prophecy, Aegon has to succeed in order for Dany to pull him down. Here’s the quote:

A cloth dragon swayed on poles amidst a cheering crowd…mother of dragons, slayer of lies.  
 
“A mummer’s dragon, you said. What is a mummer’s dragon, pray?”
“A cloth dragon on poles…mummers use them in their follies, to give the heroes something to fight.”

Aegon is on the doorstep of King’s Landing. He’s got an army, he’s got the name, he’s got Storm’s End, he’s young and handsome and charming, all that stands between him and the capitol is a Reach army that’s mostly green and full of Targaryen and possibly Blackfyre loyalists. And in the capitol, the queen regent is unstable, the boy king is doomed, and there’s a religious fanatic that would love to crown a true king with the right policies. 

The cloth dragon on poles in Dany’s vision is a Targaryen banner being paraded through King’s Landing as Aegon VI ascends to the throne. If Aegon VI isn’t King when Dany arrives, if he’s just another claimant, then the lie is incomplete – he can’t really tempt her in the same way he could if he was sitting on the Iron Throne and offering her Visenya’s seat.