That article's all shitty speculation. The Tyrion book is just quotes from the books and show so he doesn't need to write anything, he already wrote the dangerous women novella, and he's just editing that other book. Don't see why that would push him back to 2017 or whatever it said.
I'm pretty sure he's got over a thousand pages by now, last time he mentioned it he had like 600 when last season started. The reason AFFC/ADWD took forever was because he started writing the book after ASOS set five years later, then scrapped the idea after writing for a year, then got stuck trying to get all the characters where they needed to be by the end of ADWD (the meeranese knot)