I'm not overly skeptical that it could be pushed back. As of about 9 months ago I remember reading that he had close to 1500 pages of unedited manuscript written, which I thought at the time must mean he was almost finished.
But of course, Martin happens to edit a crap ton of other books and anthologies and has had his TV show to work on as well. I'm also guessing that the close proximity of the show's beginning with the release of a new book is hardly coincidental. While I'm not 100% certain that it will not be pushed back, I'm still pretty darn certain it won't.