I always dreamed the would turn it into a 3v3 or 5v5 arena brawler/shooter. Call me crazy, but the first had the feel of going 1v1 in an acrobatic fps way more than a fighting game, IMO.
Give me the same basic mechanics in Halo-eque arenas with respawning limited-use power arms distributed around the map, and allow for the grab move to be used for traversal (by grappling statues). All in all, I think it would make for an insanely fun and chaotic multiplayer experience. Would work really well with the rumored mousecon too.
Using that setup as your base, the campaign could be a corridor brawler taking out mobs capped off by boss fights in those same arenas. It could even have co-op.
Never going to happen, but I can dream...