People talk a lot about the character, but what about the stage?
I think that's where they'll bring all the characters in. It'll be like that bird dude in the Ness cloud stage, but you get a random ARMS fighter or two that join the fight in the arena. That way they can put a bunch of them in, and keep a few for the character as playable?
I think they'll do the Hero treatment, and keep the 4 most popular as alts. As far as I can tell, Springman, Ribbongirl and Min Min seem to have similar stances, so they're only missing one more.
And that way, they can reuse the Springman assist trophy as one of those guests, and from now on, have it rotate with the others when he comes in through AT. And they can base all the other fighters on that AT, meaning it's mostly a reskin job for those other stage-specific NPCs.