Ohh...now it makes a little more sense.
Yen Sid needs 7 keyblade yielders to fight the Organization XIII under Master Xehanort. I think Xehanort is going to find some new members, probably Malificent is gonna be one of them I haven't forgotten about her. Sora is off on his journey to probably find Ventus and wake his lazy ass up from Castle Oblivion or find Aqua stuck in the realm of darkness either one or both which would be cool. Lea is not in the organization anymore. So I predict the 7 keyblade yielders are Sora, Kairi, Riku, Lea, Ventus, Aqua, and Mickey vs. Xehanort and the organization. I could be wrong because there's Xion and Roxas that we have to consider and Terra probably although Terra will be saved once Xehanort is defeated. Man, looks like Kingdom Hearts 3 is gonna be one hell of a complex game.