I don't mind the idea of Vanitas taking over Sora as I could see it happening (many games nowadays love the whole "You choose between good and bad" scenario). However, I don't quite understand how Vanitas would not only get into Sora's heart...but moreso take over it. Sora's heart is quite strong so I don't see that happening. However, if Vanitas returned and tricked Riku into thinking he was Sora, I could think of some pretty interesting things happening from there. OR! Vanitas could somehow meet Kairi and make her the DiD...AGAIN!!! lol xP
Also, I really like how in BbS the characters got more involved in the worlds itself, but I still prefer the KH1 format where the worlds were semi-focused on for their Disney story but also stayed along the lines of the main story. I just need to see Esmeralda's goat!!!!!