Actually, having done some research, I'm thinking perhaps Ishgard may, in fact, comprise the entirety of the expansion. We know that "Sky" is the theme, and apparently, the Ishgard banner has thw written text "Of the Sky, From the Sky, For the Sky". It could still serve as a prelude to the expansion -- perhaps the religious leaders of Ishard "summon" a floating continent somehow -- but actually, not I'm thinking perhaps Ishgard is going to be more expansive than originally believed, making up a full Expansion's worth of environments.

Although, I still dig the idea of a flying continent! ^_^