The final books will never be written.
I think that George RR Martin has written himself into a corner with the last books with far too many open and expanding plot lines, and is neither interested nor motivated nor contractually obligated to complete them.
He's been living the good life as a wildly successful writer (not that I blame him at all) and he isn't getting any younger.
He really should just hire a team of writers to finish up the novels for him, and just attend high-level meetings to work out the final plots and goals.