Yes, 2017 is the anniversary for FFVII, I think January 27th in Japan is actually it's anniversary. Which probably is a gauge for the reason of their progress if they want to hit that day. Probably also another reason they split the game up. They realized they couldn't deliver the whole game on the date they wanted. So they're going to deliver on a piece of the promise with the promise of more to come.

What if it is open world Midgar. ;p That would take up 40 hours if they wanted to do so. But it is only like 5 hours of the game, so that's a lot of padding if they plan to do that. It'd make more sense to do the whole first continent I think, though there really isn't a good cliffhanger at that moment. The game wasn't really built around the idea of a good stopping point.