I believe that a prerequisite to joining the fight be that characters appearing in the game must be evergreen characters; that is, they must be part of a long-running popular franchise.  Using flash-in-the-pan characters cheapens the timelessness of the game.  Newbies such as Katamari Damacy's Prince and Super Monkey Ball 's AiAi need not apply just yet.  Eggplant Wizard is still too obscure to stand on his own.  Hell, we're lucky we're getting Pit from Kid Icarus at all.  Ryu has the background, but could he adapt to the wacky Smash Bros. world?  If Snake can blend in, then Ryu certainly has a chance.

Speculation being what it is, here's a sample of who I'd like to see appear in Super Smash Bros. Brawl:

• Mega Man.  Not X or Zero or MegaMan.EXE or ZX or any of the other spin-off characters.  I want the classic original Mega Man, complete with pea shooter and ability to copy other characters' powers.
• Sonic the Hedgehog.  Standing on his own, too, without Tails or Knuckles or the other two dozen Sonic characters.  Give him his spin jump and homing attack for starters.
• Pac-Man.  We can't invite timeless characters without asking Pac-Man to participate.  Can't you just picture the other characters turning blue and running away from a hungry Pac-Man?
• Melee's Young Link replaced with Wind Waker's Link.  It would make for a nice contrast with Twilight Princess's Link (who is already confirmed to be in Brawl).
• FAWFUL HAS FURY!

No matter which characters you're backing, here's hoping that all our Smash Bros. dreams come true.