1) One things for sure, it's going to be big. If SE can pull off such a large world with XII then XV...I can't even imagine. XII felt disconnected at times with the loading in and out of areas, so it's great that this truly is open world. Imagine walking / Driving / Chocobo Ridin' across the large open plains and slowly seeing a huge city appear from over the horizon *_*

2) Airships were talked about for Versus XIII but I've not yet read anything to suggest that they'll appear in XV. Though I haven't read anything that says they won't appear, either. At this point it's anyone's guess, but sadly I don't think they'll make a (playable) return. If anything I imagine a system like X where you can fast travel to a location. For all we know though an airship could be the special surprise at the end of the demo. Speculate away!

3) As Freya and Fox have said, Chocobos have pretty much been confirmed already. I'm looking forward to seeing their design!