I seriously doubt Rikku being in KH2, even though she's my favorite character. First of all, in my opinion, Yuffie already stole Rikku's clothes and her personality (as with Cloud and Vincent... <_<, I mean now these two girls are basically the same person with a different appearance. One of the reasons they took Rikku out was because of name confusion, although I can see this working for the plot also (Sora enters, someone says 'i'll introduce you to Rikku', Sora gets his hopes up, neither specifies what gender their Riku is, Sora gets his hopes crushed ^_^. Just, for Rikku, don't get your hopes up, 'cause it's probably not happening. I can see Lulu in KH2 maybe...(they would have to take away some of her cleavage, but her overall personality goes with KH2's 'darker' theme). ^_^;
You underestimate S-E. You think they would seriously make Sora that stupid and make you that stupid too? Plus the names sound different in Japan. They wouldn't just take a character out because of their name in America. That would be pointless to the Japan viewers and the people who don't care at all.
The main reason Rikku wasn't in KH was because she was already in a game at the time (FFX) and then was going to be the main character of a new game (FFX-2)
So you can doubt Rikku being in KH2 but if you are going to doubt it because of her name sounding like Riku then you should at least come up with a better reason than that.
And why do they have to put Yuffie back in the game? She doesn't have to come back. And they can give Cloud back his personality. They only gave him Vincent's personality because he was leaning closer to the dark side and Nomura wanted him to seem more demon like. So if Cloud isn't leaning closer to the dark side and isnt seeming more demon like then he can have his personality. So they can easily take Yuffie's personality away. >_>
Also Irvine has a chance of being in KH2. He was replaced by Wakka.