Apparently at Comic-Con we can expect 2 cross-over games to be revealed, each features stars from each universe in their respective engines?
That means Namco vs. Capcom would have Tekken and Street Fighter brawlers in the Tekken 6 engine where as Capcom vs. Namco would star the celebrity butt kickers in the Street Fighter IV engine. They'll adopt their respective visual styles.
This is the first time such a proposition has come up, although Capcom is no stranger to making cross-over universe videogames. There's a YouTube clip below of the major event that went down in Las Vegas, teasing a super event in the videogame space...