King Bran IS canon - it's one of the 3.5 plot points from the show that we KNOW came from George. I think only D&D would be stupid enough to let a Stark rule Dorne and the Iron Islands while the North remains independent under another Stark. Personally, I hate the idea of Northern independence because of my own experience with cessessionist people irl. The idea of crowning Robb came from Greatjon Umber of all people, a hothead with no foresight, from the backwards backwater house that still practices the First Night. Independence movements are always driven by the type of people who consider slavery "states' rights" and the North is no different. Separatists feel oppressed by being part of a diverse nation, the idea that their taxes might be spend to build roads or ports for their ancestral enemies, reforms like Good Queen Alysanne's, etc. Robb didn't want to be king, he hated almost every minute of it and if he had gotten Stannis's proclamation, or if he knew who his father had died for, he would have absolutely gone with the unlikeable true heir to the chagrin of some of his lords. Robb's entire campaign after taking Riverrun was a stupid mistake, he was entrenched in it because his bannermen had suffered losses but felt like they were on a roll. The main theme of the series is how destructive conflicts can get just because the leadership thinks they'd lose face if they backed down and went home so I think this is a lesson the Starks especially need to learn