Two super bars instead of just the one we've seen up until now. 2 players on the same team, maybe, with a bar for each player?
Edit: On a side note, there are gameplay videos uploaded to CapcomUnityVideos YT channel. One fight (Poison & Nina vs Ryu & Ken) takes place at a skate park. You can see Yun skateboarding in the background and Yang watching. So, maybe they wont be in.
Edit 2: A cool musical touch in the game. When two Street Fighter characters are on a team and are both on the screen at the same time or doing a tag team ultra, the Street Fighter II theme tune kicks in.