@bigjeffrey: Well, it'd have to fail on indie game terms, not big budget retail. If it does, maybe the whole platforming fighter sub-genre is damned to live and die by Nintendo. I'd find that discouraging personally - I don't like waiting 6 years for a new one. It's doubtful any big publisher will try again after PS All-Stars flopped.
So if this is Like a arc systems game is it similar to guilty gear isuka? Cause y that's the only thing I can think of as a 4 player game.
It'll probably work out more like Smash Bros given the people involved (ie: some top level Melee/Brawl players and a Project M coder). There's an article that basically confirms they're using a similar knockback and ringout system. A good thing IMO, since it plays to the team's experience and those mechanics tend to be left out in most Smash 'clones.' Bringing them outside of a party, mascot fighter context is still relatively new idea. Certainly it's taken long enough for someone to take that ball and run with it.
I'm guessing there will be some overlap from traditional fighters as well. Mike Z is consulting with the mechanics. They've also said they're going with 8-way directional controls to accommodate fight sticks. Been some murmurings about on-hit-canceling and such as well. (ie: Lucario in Project M)