One other thing, thinking about it the Mii might not make it in. Why? I think Nintendo wouldn't want gamers beating the crap out of caricature versions of other people.
Before anyone says anything, yes I know SSB has cute characters beating each other senseless, but these are fictional characters that hail from games where battle is common places.
The Miis, however, were made just so you could insert yourself into fun activities like sports, fitness and music.
Also, Nintendo DID remove the GB camera feature from Perfect Dark because they feared that people might accuse them of promoting violence.
So add those things and it makes the Mii an unlikely character.