I imagine for as great as Bran is 'supposed' to be, having someone succeed him will be hard and a very hard sell for that group of regional leaders to agree upon.
I really thought the 7 kingdoms were going to become 7 separate kingdoms, like what Sansa did with the North and they all agree to sign some sort of confederacy agreement - to not war against each other, ever, or the others would immediately come to whoever was attacked's aid and they'd squash whom did the attacking.
The Greyjoys are warriors, they'll want more than their lands. And while I ADORED Bronn, (Jerome Flynn is an amazing actor), that he not only actually gets Highgarden but is on the small council? He'll likely go to war with someone... probably over a woman.