I don't have a link in front of me, but I remember very vividly that I read an interview mainly about 358/2 Days in which Uematsu was asked about Kingdom Hearts III. He replied that he hadn't thought of it yet and that he won't start working on it until the cross-platforming is finished.

Also, there's no way Kingdom Hearts III will be on the Wii. I don't doubt that Square would make a game for Wii, but Kingdom Hearts III will be on the Playstation alone.