Thing is, this book isn’t even going to have the ending yet, and at this point he doesn’t exactly have a high bar to clear to make improvements on how GoT approached the ending. There’s also nothing wrong with outright making changes to the ending if he wants.

He’s clearly been in his own head about the series ever since after the fourth book. He still likes writing about the world, so my best guess is whatever progress he makes on Winds is occasional efforts to try to shed that emotional weight and free up some headspace for the side stories he likes more.