Boy, I haven't seen this topic in a while.
There is already pretty much an Adventure Mode II: All-star Mode.
Maybe there could be a racing game built into the next SSB, or even better a mini-game mode to earn trophies and game goals, hm?
Basicly, I see no way (after playing SSBM recently) that SSBM could improve. For being one of the first games on GC, it had steller graphics and the fighting action was hard core. One problem for a SSB on the Rev. is fitting it in with the Rev.'s odd controller. I have no idea how they could pull it off, what with two A & B buttons instead of a C-stick or X & Y buttons, along with L & R to grab. However, I have confidence in Nintendo.