Well, alloys and wireframes enemys were just skeletons of the original fighters in the game, like Peach and Captain Falcon, so putting Miis in multi man melee doesn't change that much.
What is fun is, if it gets the Miis created in your system and randomize the special attacks, it will create a very challenging and new mode, where the chances of get the same mii fighting agaist you be very slim ( 3 classes x 4 special moves x 3 variations, aside the size modifier).
If not, Im sure the system will have pre-builded characters to use ( like 9 different fighters, swordsmans and gunners). If it ends this way, it still be like old multi man modes, where we fight characters that we know how will act (they will probably have always the same face/shirt color so you can recognize them). I hope that if it comes down to this, that the mode can read at least the Miis you create.
That way we only lose the looks of wiereframe, but hey, there is always alt pallete. Little Mac can have one, why don't everybody else can't?
