I about wrote her up, actually, but I decided to stop at pure Nintendo characters, because otherwise I could probably still be writing.
I bet if Capcom is going to request a guest character, most fans, and Capcom itself would pick a version of Mega Man first. IGN, which for some reason apparently thinks the game or games should be Nintendo Vs. Capcom didn't even include her on their poll, though that's mostly because they're idiots, rather than a reflection of Amaterasu's actual chances. Speaking of the vs. Capcom games, though, Amaterasu did appear in Marvel vs. Capcom 3 while Mega Man didn't. A version of Mega Man, however, did appear in Tatsunoko vs. Capcom, which was the Wii exclusive, with two other Mega Man characters, Roll and Zero, while Ammie rode the bench on that one (though Okami final boss Yami was the also final boss of that game).
The other problem is that we don't really know if Nintendo is going to allow guest characters; last game they only let in Sonic and Snake because their respective owners asked them, rather than Nintendo extending invitations. The "rules" for last game were that a guest character had to have an appearance on a Nintendo console and be originally intended as a video game character (so, Mickey Mouse, for instance, would be ineligible). Basically, the Super Smash Bros. series is one giant free advertisement for Nintendo and its games in addition to being a bestselling game itself; I wouldn't be surprised if Nintendo caps the "guest spots" at two, just to allow itself the most free advertising (Sonic and Snake's appearance, for instance, actually ended up giving free press for then recent Xbox360 and Playstation 3 games that did not appear on any Nintendo console).
I about wrote her up, actually, but I decided to stop at pure Nintendo characters, because otherwise I could probably still be writing.
I bet if Capcom is going to request a guest character, most fans, and Capcom itself would pick a version of Mega Man first. IGN, which for some reason apparently thinks the game or games should be Nintendo Vs. Capcom didn't even include her on their poll, though that's mostly because they're idiots, rather than a reflection of Amaterasu's actual chances. Speaking of the vs. Capcom games, though, Amaterasu did appear in Marvel vs. Capcom 3 while Mega Man didn't. A version of Mega Man, however, did appear in Tatsunoko vs. Capcom, which was the Wii exclusive, with two other Mega Man characters, Roll and Zero, while Ammie rode the bench on that one (though Okami final boss Yami was the also final boss of that game).
The other problem is that we don't really know if Nintendo is going to allow guest characters; last game they only let in Sonic and Snake because their respective owners asked them, rather than Nintendo extending invitations. The "rules" for last game were that a guest character had to have an appearance on a Nintendo console and be originally intended as a video game character (so, Mickey Mouse, for instance, would be ineligible). Basically, the Super Smash Bros. series is one giant free advertisement for Nintendo and its games in addition to being a bestselling game itself; I wouldn't be surprised if Nintendo caps the "guest spots" at two, just to allow itself the most free advertising (Sonic and Snake's appearance, for instance, actually ended up giving free press for then recent Xbox360 and Playstation 3 games that did not appear on any Nintendo console).