This is actually smash brothers. That's actually hilarious.
What they've shown and said sounds safe. Character roster is Kratos and people you'd expect, and then Parappa to say "see we're bringing in old favorites!" and Fat Princess, "it's a semi-obscure character!" Action looks like smash bros, physics and all, only with a twist to win. Attacks only serve to charge up your super meter, and the supers are the only attacks that matter. So it's like Dissidia, only there's no health bar. The system in smash is because it's a versus platformer game and the entire goal is to stay on the platform while knocking the other guy off. It balanced attacks by making fast or ranged rapidly decrease an opponent's defense, while the slower attacks knock them away. I don't get what they're going for.
Doesn't look bad, surprisingly. It looks polished, stages are kinda neat, and with a name as stupidly generic as All-Stars Battle Royale, it looks competent unlike Move Heroes on the Move. It's just...Smash brothers. I like smash brothers, but I would've liked an arena game like power stone or gundam vs gundam.
And I don't think they'll go crazy with the fan service like they need to. Smash Bros Melee went stupid and had Ice Climbers and Mr Game and Watch. Sony doesn't have as great a history as Nintendo, but no one cared about Ice Climbers, or Pit from Kid Icarus, or even knew who Marth was, or Ness, but they were still in there. Have a guy from Genji summon a giant enemy crab as a special. Really stupid stuff like that. Dark Cloud people, the father from incredible crisis, a space ship from colony wars fighting omega boost.
edit: read something that said third party characters will be in this too. that makes it better, maybe.