Throne will belong to the powerful one. Stark don't have birth right on Throne.
Interestingly now R+L=J is almost confirmed. Only remaining Stark is Bryan.
Might be possible... But as there are only 2 seasons and 15 episodes(As roamers suggests) left. I believe everything in the end going to be related to white walkers.
That is related to what Stanis told him during season 5. "Keep reading Sam".
I believe he will read and find something secret about white walkers which is unknown. Also it might be related to creation of some weapon to be used against white walkers.