Someone call Mr. Martin and tell him to get cracking on that 6th book
Check out westoros dot org, or GRRM dot com. He's already released 2 sample chapters from the WoW, as well as he read one aloud at a convention, about Ser Barristan Selmy fighting in Essos with Danerys's forces, and it's been transcribed on the web more or less exactly as it was read. So, if 3 chapters have been released by Martin, he's got to be closer to finishing it than he was with the 5th book at this point in time, 2 years after release of the previous book. Dance/Dragons took 6 years to complete. If Winds of Winter was to take that long, HBO would have a big problem, having portrayed the ending of the books long before the 2nd last book was even printed.
They are obviously splitting the 3rd book into 2 seasons, as the entire Martel's/Tyrion's Trial/Fight at the Wall hasn't come to pass yet in season 3 of the TV series, so by the end of 2014 they'll be someplace around the start of Feast/Crows. That 4th book was a major drag IMO, very slow compared to the previous three, and pretty tough to stretch out past a single season of TV, at least at the pace they do the episodes at HBO. So, if the 5th book was to air on TV in 2015, that would mean that the fall of 2015, when they need to be shooting the 6th book, the book will NEED to be in print and out there, or else they run into all kinds of issues, obviously. That gives GRRM roughly 2 years to finish the 6th book, which he looks to be well on pace for, which makes sense as I can't see HBO risking their cash cow on the whims of a writer who is legendary for blowing deadlines - they would have contracts in place ensuring he didn't do this, AGAIN, haha.
I've read on GRRM's personal site, in his "not a blog", that rumors are flying that there MAY be a splinter TV series, again done by HBO or one of its lemmings, dealing with the time of "Robert's Rebellion", or the "War of the Usurper", 17 years before the current time frame. I think this would be most excellent if true.
