Gnarleysquid
Smash Apprentice
My reasoning for that statement was derived from Sakurai's initial comment pertaining to the way in which the roster was decided.I second this, I was also impressed by the responses in quotes especially this one,
If Mewtwo isn't confirmed in the final roster before the 3DS title release date, then he could probably / definitely be guaranteed DLC plus any other cut characters!
Edit: Also thanks for the link @ Gnarleysquid
“All of the characters you see here and pretty much all of the characters that we’re still looking at have… were all decided right at the very beginning of development."
Those that believe in the Gematsu leak will also know that the leaker allegedly confirmed that DLC is coming, which appears to be supported by Sakurai's statement. If Mewtwo isn't included in the initial roster, then there's no reason it wouldn't be locked in as add-on content – unless Sakurai has opted to just leave the character out of the series going forward, but that just doesn't make any sense.