He can't put it off that long because the TV show will catch up. The shows film in the latter half of the year and air the following year. The second half of SOS will be filmed in late 2013, FFC will then be filmed in late 2014, and DWD filmed in 2015. This means WOW will need to be filming in late 2016 and don't forget the screen writers need time to compose screenplays before filming so they will need new content from GRRM before then - so perhaps early 2016 at the VERY latest. More realistically, 2015 - or if you're optimistic, 2014.
Unless, of course, the books get split over two seasons again like SOS is, which would tag on another two years but I haven't heard plans for that and GRRM can't exactly cross his fingers and hope they do. But even then, filming for WOW would commence in late 2018. In that case, it would have to be released in early 2018 at the VERY latest but more realistically, it would be earlier.
2019+ is just unrealistic unless you think they might start splitting the books over more than two seasons. But again, I've heard of no plans for that and GRRM can't exactly rely on that.
Splitting another book into two shouldn't matter - we should still get the first half before 2016/2018 if the TV show hopes to continue.
Unless, of course, the books get split over two seasons again like SOS is, which would tag on another two years but I haven't heard plans for that and GRRM can't exactly cross his fingers and hope they do. But even then, filming for WOW would commence in late 2018. In that case, it would have to be released in early 2018 at the VERY latest but more realistically, it would be earlier.
2019+ is just unrealistic unless you think they might start splitting the books over more than two seasons. But again, I've heard of no plans for that and GRRM can't exactly rely on that.
Splitting another book into two shouldn't matter - we should still get the first half before 2016/2018 if the TV show hopes to continue.