yes, I've heard about that, but I thought KH Final Remix was going to be like that. But I guess the rumor was wrong. And I don't think you will use Riku this game, since he is kind of locked up with King Mickey in Kingdom Hearts and the game ended (SPOILER BUT O WELL) while Sora, Goofy and Donald goes out to find Riku and King Mickey with Pluto the dog... and Kairi is waiting for Sora to bring back Riku with him... so I'd say it's still going to be Sora but with FF worlds.

Or on the other hand... it could be like Riku with FF characters as his team instead of Sora and disney characters. But my first prediction is more likely unless they make MORE than 2 games to KH.