[@Greenie] Look forward to reading it! 

[@bloonewb] It's a pretty good sheet, but I have just a few minor quibbles. 

1) I think it fits more that Jon would have taken on the Boltons after Stannis had a go, like in the show with the Battle of the Bastards. I can't really see Jon running to Daenerys for help instead of rallying his forces and I find the idea of Bran leading an army well... unlikely to say the least. I feel like the Boltons would have been taken care of before Daenerys landed on Westeros and things ramped up with Cersei. Plus since this is trying to stick to canon, Jeyne should already have been in Stark custody since she ran away with Theon. 

2) It doesn't seem likely that the child would have just been sent away with the Starks just hoping for the best. That basically never happens when a child potentially poses a threat. Realistically, he would have been taken as a hostage and raised with the Starks. He might have been given a castle of his own, and this could be that Castle Ethering (I see no reference to it in canon). 

3) So he wouldn't have the Dreadfort but he'd still vie for it. Your concept made him seem more like a manipulator than a warrior, so it would make more sense for him to be scheming instead of leading an army. Like he's pretending to be a loyal vassal but he's really planning on betraying the Starks, just like Roose. That's more believable than him somehow suddenly finding out he's a Bolton, somehow proving it to a bank, and than somehow marching an army big enough to besiege a major castle without any warning from the spies the Iron Throne has. It'd also improve his long-term survivablity a lot since I don't think a rogue lone upstart would survive a one-man war against the North and the Iron Throne. Especially since he's supposed to be smart, I think he'd rather scheme than jump straight to conquest. 

Alternatively you could have him be more subtly vying for the Dreadfort by trying to get in the good graces of the Starks and Targaryens instead of trying to undermine them or openly rebel. So he might be kind of loyal but also looking out for himself above everything. Also your character can have a sweet ancestral flaying knife. 

That's just my thoughts on it, otherwise I think you have a good concept.