There's Capcom VS Sega VS Namco Bandai coming to the 3DS.
And Namco Bandai is making the next Smash Bros. at least the 3DS version...
And they won't bother with Mass Effect cause 1. Nintendo and EA, aren't in the best relationship at the moment, things are ice cold between them... 2. there's only been one Mass Effect game on a Nintendo system and it was a half-assed port... and 3. Snake comes from a series that practically makes fun of itself within the game itself and Sonic is a no-brainer. Mass Effect takes itself too seriously to be any part of Smash Bros. a game which is just full of silliness.
That said, if I were to have any character from any game be a part of Smash Bros. it'd be Master Chief... just think, Mario vs Sonic vs Snake vs Master Chief. You know you all want it.