You know, I never mentioned much of anything about Birth By Sleep.
It seems that Aqua somehow disappeared. I guess they're leaving her as a surprise. I know she was one of Ven's closest friends, so I doubt she'd be a minor character.
Terra/Ven will obviously be the new Axel/Roxas. GAH.
And judging from the "Please erase me" part, it seems that my previous theory on Ven/Roxas still stands. For those who forgot, my theory was that Sora met/knew Ven at one time, and when he became a Heartless, "Roxas" was born out of Sora's memories of Ven. Sora was probably supposed to forget all about Ven, but it seems like he never did. Once Roxas "merged" back with Sora as a "shadow self", he simply became just another part of Sora rather than simply memories of Ven.
Where would Ven be though? If it's called "Birth By Sleep", then it might mean that Sora's abilities as a keyblade wielder(shown in the first Kingdom Hearts), woke up once Ven was "frozen", or "put to sleep" by Old Man Ugly. Hell, he might even be Sora's older brother.
Right now, it's just a bunch of who on earth knows?