That's an inevitable issue with splitting A Storm of Swords
over two years: it's all one book, with one story for each character. Arya, for example, has all of two chapters after the Red Wedding, which will have to expand to cover a large chunk of season four. Bran has a grand total of seven chapters across all of Storm
, which will somehow be stretched over at least three seasons. I live in fear that Benioff and Weiss will address this by contriving more original material, at which I don't think they're particularly good.
I really don't seem them putting the Purple Wedding in season three. Once that happens, you've got at most four episodes' worth of King's Landing plot before "Lord Tywin Lannister did not, in the end, shit gold," and that's a bit early to be reaching the end of A Storm of Swords
. I tend to think a lot more time will pass between the Red and Purple Weddings in the TV show than did in the books, so that we don't get the latter until around the middle of season four.