One Piece volume 80 looks scheduled to release on 12/28, making 2015 a four volume year.
http://blog.livedoor.jp/onepiece_figure/archives/54526736.html
Since Kaido is revealed at the end of volume 79, Zou should definitely be in volume 80, but how much of the first part of the arc will be in it?
Update:
Confirmed on Shonen Jump's website too.