Iko MattOrr
Smash Champion
IMO it's a very borderline case, and it's very much subjective. It depends on what Sakurai thinks about it. Regardless, nothing has ever been set in stone with Smash so far, so even if exceptions never happend, they can happen some day.The only issue with that is that there never have been "exceptions", Miku not originally coming from a video game immediately means she has no chance now or ever in the future. This is like the Agumon debate, but at least Agumon's tamagotchi toys have some credence to it as video games, like Game & Watch.
I'm not arguing in favor of Miku or anything, I don't care really, it's just that I think that she's not completely impossible, despite being the mascot of an audio software and not directly a game character (even though she still has her own gaming franchise too).