Hmm. Well Super Smash Bros. Unite could be a good one. Still sort of fight oriented, but could be a good reference to online and wifi interactivity if they have it. Also could be about how they eventually have to unite their powers to fight a common enemy like with Tabuu. I would prefer SSBrothers Collide. The colliding of worlds. And systems. Even the symbol shows that.

Good characters I would like to see:
Commander Keen
Pac Man
Sly Cooper characters (I kknow they 99% won't have that happen but if I could make one most impossible wish)
Crash Bandicoot
Ray Man
Bit.trip characters.
Tron characters. Like Clu, Rinzler, and Quorra (as much as I don't want them to integrate movies since they might go overboard, these would be a plausible choice)
Spore Wars
Prince Of Persia
Ninjabread man, why not
Earthworm Jim

Others of course. Now before you begin to scoff at all my ideas, remember that you wouldn't only be getting the character, but also cool and stylized levels and weapons and music and assist trophies. Sly would be great for that. I know the ninjabread game didn't do well, and I never played it, but his moves from the trailer and items show he could have a unique visual style to the game. Now that you can take pictures, visual diversity is a must.