Yes. How much you it is is up to you (in reality the producers) but yes. And there are probably other issues people can think of easily. Hell, I'll throw one: Programming. Not that I'm saying this would have happened, but it can* (I go back to this later)
It's for sure not nitpicking. In a game of Nintendo All-Stars and then some more, seeing it that a character that's just basically "Yourself" as not a Nintendo All-Star, a lack of novelty, and a lack of interest is totally plausible. And here's a catch-22: It's happened before. Super Smash Bros. Brawl says hi. That's not to say characters who got rejected last time can't be in this time (K. Rool, Krystal, Ridley, Masked Man, Daroach, Some Fat Biatch I don't know, etc); we've seen it with Villager and to an extent, Mega-Man, but it's for sure happened.* (With the *, the reason Mii's could have been discluded is because Wii hardware is actually not that great for doing something like that where-as Wii U has proved perfect. Thus, I've partially debunked my own argument, zing)
And no the Mii itself is really not a nintendo character. Maybe the aesthetics and the name but that's really it when you get it down. Not that I think they won't be in this installment. Even before the rumor and before the announcement's I've taken it seriously (Yes I know probable character roster will say otherwise shut up).
Though it's not all sour. If recent things are anything to base off of, it'll probably only have a changeable shirt and a changeable head, which won't be that visible. If it has a moveset, sure, **** it, whatever. It bakes the question "What's the worst that'll happen" and the worst is you have a party of Smash Bros and one of your friends takes twenty minutes designing a penis mii while the rest of your friends just want to play the damned game.