They could just slap a 2x2 or 3x3 versus mode (like Marvel, switching chars, or KOF, by waiting line) as an optional feature while keeping the core game 1x1. It would be awesome.
Also, EX3 > SFV (to me).
Yeah, a Team Battle would be great, especially if they added some sorta feature to it like tag skills or moves. Just having the feature will probably get overlooked. I think Mortal Kombat has has had it and it feels like modifiers (Tower buffs) get more enjoyment.