Square Enix has reiterated that they have no idea what their new MMO is going to be at a Final Fantasy XI fan event.
Vice President of Square Enix, Hiromichi Tanaka, said:
As you might already know, members from the current FFXI team are working on a next generation MMO, but it still hasn't been decided whether that's going to be a game in the FF series, a continuation, or a totally new game. We are working on it, but it hasn't been decided that far yet.
Game development usually doesn't work like this. Games are usually made knowing what the story will be and what franchise or universe it will take place in.
Regardless, Square Enix is officially "Wingin' it".