I am working on a theory that has Davos ruling/leading at the end, not on the IT though. Here's the basics of what it involves:
(IF D/D follow what I suspect might be George's ending):
--Tyrion does indeed betray the Starks (not Dany, she is still needed as a tool to his ends) and he will be tried and executed.
--Jon and Dany will live and so will Baby, but they are going to change throughout the course of the season and not be the same people we love now, by the end. In the end, there will be no "heroes/good guys." Not even Jon. And after all this, all the moral compromises they have had to make, and the further losses that both will have to endure, they betrayal and having to execute Tyrion will shatter them. They decide that the most important thing they both want is a family (as this is the most important thing they really want in the books, if you read carefully) and they decide to take Baby and go into exile and leave Westeros. Thus they are not the Arwen and Aragorn, but the tragic "Frodo" figures, "Sailing over Sea."
--Considering how many times Jon has been merciful and granted (limited) clemency to people who have done horrendous things to his family (Theon, Mel) the betrayal would have to involve something pretty horrific that hits Jon at a deeply personal level. Not just the destruction of Winterfell and Westeros in general. It has to hit close to home for Jon to want to execute someone who was his best friend. And the method of execution might be savage. So you can imagine after all this, he just say "f It, I;m done with this."
So far so good. But here's were it would be unsatisfying, esp to Targ Restoration fans:
Martin might end with the ultimate cliffhanger: Davos left at the end, and after the trial he decides to take up the mantle and rebuild Westeros. But how? And why Davos? This is the part I am working on facts to support, I will have this theory up in a week or so. IMO Martin is uniquely positioning Davos in the books to rule right under our noses and we don't even see it. And he has an outsized role in the show too.
The cliffhanger would be , we don't know what Davos does and maybe we never will. Maybe in the books we find he melts down the Throne, but not on the show. And we never get to find out what happens when this commoner takes over. How much power are the smallfolk allowed if any. How exactly does the system of govt work. Just as we never get to see Aragorn rebuild ME, we never get to see Davos's rule of Westeros. we are left asking questions about what happens next. Of course "Spring" il come in a physical sense but we'll never know if it does in the political/social/real GOT sense. And that's the real question of ASOIAF--how does it affet the human heart.
And then there is the question of the NK. I'm sure his tale is not "Our Superheroes Jon and Dany and Bran and Mel take him out, now all is great, yay, now they can get their just reward and rule."
we will never find out if the Wheel is truly broken.