Y'know, an interesting thing that the "Oil vs Water" trailer highlights is that... Street Fighter X Tekken seems almost like the various [DC Hero] VS Predator/Alien comics in that, it's a cross-over but one side are good guys while the other are bad guys.
Think about it: For the male leads on the Street Fighter side we have Ryu and Ken. They're basically good people who fight honorably and for a deeper self awareness. On the Tekken side, we have the Mishimas. A family who's main characterization point is that they inevitable will become evil douchebags (PS: **** you, Tekken 6).
Hell, it even applies to the female leads. Street Fighter has Chun-Li, who's an Interpol agent fighting to stop crime and who's ultimate dream is to bring her father's killer to justice once and for all. Tekken has Nina, a money-grubbing mercenary who's ultimate dream is to murder her fraternal twin sister... just because.
It'll be interesting to see how this plays out, story wise, and how Namco will respond with the story for their version.