I can agree with Markus, in the sense of combining both 64 and Melee for Brawl. There are so many new things that will make this game good, but in a sense, it doesn't seem it will be taking a big step from 64 or Melee, in the sense of battle. With new features, such as online play, there is your big step.
So what if people switch over to Brawl to play a majority of their Smash on it? After Smash64, most people switched over, for those who owned GameCubes. The same goes for now, people who own Wii's will most likely switch over to Brawl, but Melee will still be played, maybe not as much. I bet most people that run sessions will switch to Brawl, and still have Melee to play, but it will be the "side" game, unless a majority still wants Melee to be the "main" event, just such as Smash64 is still the "side" game of sessions.
Like Markus, if you think Brawl is crap, don't even pick up the controller.