It's been five years since the last book. It's been a year since the last update. We're only two (short) seasons away from the end of the TV series. Maybe it's time to face it: it's likely the A Song Of Ice And Fire books will never get finished.
George R R Martin has even confessed that he's terrible at finishing things. The first line of the forward to his Dreamsongs anthology starts: "My career is littered with the corpses of dead series." Ouch. He goes on to recount how he's never actually finished a single series -- most ended up as single books that were intended to be a stepping stone to something more, but just never got continued.
I'd say it's entirely possible that A Song Of Ice And Fire could become one of those dead series.
George R R Martin is notoriously prickly on this issue, of course, and is quick to tell people what he thinks when they question if he should be writing faster (or more). He's also spoken a little about his working habits, saying that he can't write on the run and will only be making progress if he's at home in his office. And considering how many conventions and events he seems to go to, that doesn't happen often. While I'm all for George to work the way he works best and to write at the speed he wants, I'm just saying this -- maybe we should stop expecting more ASOIAF books soon (or at all).
HBO is preparing for the eventual end of Game of Thrones by developing not one, not two, not three, but four spinoffs set in that world.
There's also the book itself to consider. The world and story of A Song Of Ice And Fire is huge and complicated. That's part of its appeal -- but it also makes it a bitch to write. He's lost track of his own world to the extent where he has to consult the ASOIAF fan wiki to keep continuity. With all the time they've been left to ponder, those same fans have (probably) worked out most of the twists that are yet to come in the books.
While Martin is determined to write out the epic in full, with his convoluted storylines he may have written himself into a corner. The TV series had to cut out a lot of book content to navigate this tangled mess, and even it didn't manage to do it elegantly. Not to mention, the story is so huge there's absolutely no guarantee the series will finish up in just two books -- even if those two books get written. It was originally meant to be a trilogy, after all.
George R R Martin has been writing (or not writing) the A Song Of Ice And Fire series for 21 years. Looking at his body of work prior to Game Of Thrones -- an eclectic, lively mix of short stories, novellas and novels in every genre under the speculative fiction umbrella -- I wouldn't be surprised if Martin is, frankly, bored with the epic fantasy series. Maybe he's itching to move on to something new, or back to an older story.
So maybe A Song Of Ice And Fire will never get its ending. And maybe that's okay. Whether we get it or not, the story has been passed on to the showrunners of the hugely popular TV series, and in that form we will get our ending. If the last season is anything to go by, it'll be a good one too.