I was kind of hoping for Capcom vs SNK 3 instead, but this is still pretty exiting. Yoshinori Ono, producer of (Super) Street Fighter IV and SF x Tekken, said that he is interested in making Nintendo vs Capcom
http://www.nintendoworldreport.com/news/24828
If it ever does happen, there should be 2 versions: a Capcom one with Street Fighter gameplay, and the Nintendo version should be more akin to Super Smash Bros. gameplay. Anyway, what are your thoughts on this?