Inside Out "World" Proposal: Sora has the means to awaken Ventus after exploring the other Disney worlds & returns his heart to him. When Ven still doesn't awaken Sora dives into Ven's heart much like Riku did in Sora's to sort out the problem. Since KH2 made it clear that emotions are tied to hearts, Sora meets Ven's 5 emotions: Joy, Sadness, Anger, Disgust, & Fear. Inexplicably Ven's emotions look identical to Riley's because hey, gotta have the actual main movie characters in this to count as a Disney world right?
The 6 of them discover the reason why Ven isn't awake yet: the Vanitas half of his heart has also returned & Vanitas' Will is making a last ditch effort to gain control of the whole being again. Vanitas kidnaps Anger, Fear, Sadness, & Disgust; their negative emotional attributes serving to recharge his powers. This leaves Joy as the guest party member, venturing with Sora across the different islands of Ven's mind. Along the way they encounter unverse as the world's enemies, rescue the other emotions who are held at different islands before finally tracking down Vanitas & having a final showdown with Vanitas himself. Possibly the final showdown chronologically, though Xehanort could still pull a time-warped past Vanitas for the endgame.
No?
