What is the Ashford tourney theory? And why do you not believe it?

Here’s the Ashford Tourney Theory.

I don’t believe it for a couple reasons. 

First, sheer proximity argues for Arianne in the Stormlands marrying Aegon rather than Sansa, all the way up in the Vale. 

Second, in terms of character arcs, Sansa’s is about going back home to Winterfell (hence the snowcastle, hence Baelish’s plan), whereas Arianne and Aegon is about putting paid to the Lannister regime. 

Third, as with the whole Dance of the Dragons is going to repeat itself exactly theory, I think it’s too cute by half. GRRM’s a gardener not an architect. Sure, he likes to drop hints and there’s the threefold revelation thing, but to have the whole plot driven exactly by a short story that the main audience hasn’t necessarily read isn’t good writing because events will seem to come out of nowhere without roots in character.