Going by the (somewhat reassuring) latest interview, tt's probably going to be something like:
Episode One - Only Midgar, but massively expanded - Mid 2017
Episode Two - All the way to a certain death - Mid 2018
Episode Three - Until the ending - Mid 2019
All of them lasting 30-40 hours , priced at $60.
Midgar is an easy choice for taking most of the extra content. It's easily the most iconic part of the game and went by too quickly on the original release. Vincent will probably be expanded on too.
Obvious candidates for the axe: Red XIII dressing like a human and the Fort Condor minigame.