IGN: Does this pave the way for Sonic and Mario starring together in other games?
Laurent Fischer: We've spent a long time finalising this one and we're not thinking about the next game, just yet. The Olympics just seemed like the right way to bring them together.
IGN: So we won't see Sonic appearing in Super Smash Bros. Brawl?
Laurent Fischer: That's not on the cards at the moment.
Mike Hayes: Really, we felt that the Olympics provided a neutral ground for the two stars.
Laurent Fischer: Yes, the Olympics are something very special. If you have ever been to the Olympics it's amazing to see the spirit of the people watching the events - people share in a very special moment. That is something we want to recreate with Mario & Sonic at the Olympic Games.
Full article - http://uk.wii.ign.com/articles/776/776878p1.html
looks a wee bit on the negative side. I'm still hopeful though.