Adventure mode.I'm sure at the very least random matches that possibly don't showcase hidden characters should be fine.
I wonder what Sakurai has planned for the WiiU release to entice people to go twice? I know it's HD, blah blah but I mean mode wise. What could you possibly add to it besides maybe a custom stage maker? A more fleshed out story mode perhaps?
I don't think it will be revealed until 3ds gets its sales in.