I don't think this will happen, but I think it should.
In Melee, there are some battles that have characters only be able to be fought in certain places, like ex, the wire frames, you could fight them, but couldn't play them, well, in Brawl, I think that characters you can't play as, should be playable in normal fights, but not SSE, or classic or whatever, just for fun fights. But the characters I mean is the characters you fight, not characters you can kill with a jump, or a press of the A button.
Who agrees?
Let me comprehend this... so you mean like Lizardman and Assassin in such in Soul Calibur 2? I'm not adverse to that, but it wouldn't really work for many non-playables because they don't have complete movesets. I suppose there's hope in the Fighting Alloy Team, but not much beyond them.