As a reader, I am not sure I care if George R. R. Martin wants to surf a little and travel and maybe write other stuff before finishing up A Song of Ice and Fire. If it were me, as an author, I would have the events of the remaining story framed up at least. If there are five of seven books published, then it's not hard to know what happens in the last two.
I'm thinking of all this because Anisa A. Claire asks, "Where in the World is George R. R. Martin?" - which I take to mean roughly, "he's old and had better not take seven years a book to finish out the GOT universe." As for Martin, I get the sense that hyper-focus on the one project for decades is not all its cracked up to be. If you look at creators like Rowling (who spent roughly ten years doing one thing) they are now spent ... and are looked at with some skepticism.
However, the books are a big soap opera. The built-up expectation of the public is a lot to deal with. The soap is leading to spectacular, all-out war with the creatures of the true north, who will invade as far as a good cold winter will take them, maybe Dawn, maybe more. It's a soap and my favorite soap of all time. I admit to hoping for an ice dragon that will face off with Drogon, wiping out half the continent in their contest. However, whatever the finish is, it will not be big enough, because the reader will think, "Seven Hells, you just cancelled my soap. Bastard." I digress.
As for Martin not wanting to have his baby in any other author's control, well that may be out of his hands to some extent. It depends on what kind of license he will grant for a post-Martin GOT universe of books, games, movies and the possible spin-offs. Jordan wrote till he died and Sanderson did just fine with picking up the sword. Lucas licensed his all beyond the capacity for any one fan to take it all in and then gave it away (although I think he got some money). Even older book "franchises" (Wizard of Oz) had new contributors.
Other "properties" ... not so much. Is anyone writing LOTR universe? No. Christopher Tolkien has been quoted saying, "The chasm between the beauty and seriousness of the work, and what it has become, has overwhelmed me. The commercialization has reduced the aesthetic and philosophical impact of the creation to nothing. There is only one solution for me: to turn my head away." If Martin follows a similar line of thinking in the next twenty years, either directly or through his estate, then it will be a loss.
Although, I would argue that, by then, the public will recover and produce something new and more relevant. And by relevant, I mean that all the sensibilities played out in Ice and Fire books are a product of this generation. The books would not have resonated with us a hundred years ago, and may not yet, even twenty-five years from now. I digress.
The lasting creations from such weirdly diverse creators as Baum, Tolkien, Lewis, Roddenberry, Lucas, Jordan, Sanderson and even Martin--they never were and never will be enough to satisfy our imagination and lust. There will always be more. We should not slight the authors (or their estates) for how they think of or treat their babies. There will be more.