According to Kh-Insider, rumors have just been popping all over the place about the new Kingdom Hearts game. Right now, being a "prequel" seems to be a popular guess.
Okay, I can buy that, but a prequel of what, exactly? Of Kingdom Hearts the Original? I mean Pre-Sora PERIOD. Between Chain of Memories and KH2? The Fall of Hallow Bastion? Many people claim that it's the year between Sora being asleep and Roxas being in the Organization, and I think that makes the most sense.
Still, it could be just about anything, really. How about the "Elders" of the Organization? How did they do the things they did? The Knights? Where did they come from, and who were they fighting? Maybe before all of that? Ansem the Wise?
It'll be awhile before anyone knows, I'm sure, but I think that it would end up being a prequel to Kingdom Hearts 2 since Axel/Roxas is so insanely popular.