I would be shocked if this book is published before 2018.
Really?
I am much more optimistic. If you take Martin at his word, and he truly was working hard to get TWOW out before the end of April, it would seem likely that he is a minimum of 75% finished by now. This also takes into account the number of chapters he has pre-released and chapters that were diverted from DWD to TWOW due to it (DWD) being too long.
I suspect that the release will be prior to the end of 2016, but will be very surprised if it is not out by the end of 2017.