Melee is probably my most-played game, and I am utterly loving this.
If Snake's in it, I don't see why Sonic (at least) shouldn't be. Just 4 new characters, with one of them actually Samus but minus suit? Please. How many new characters were in Melee over SSB again?
Yeah, I hope Ganondorf will be the Wind Waker version, as I hope will Young Link.
There is only one potential problem I foresee:
This looks hideously like a Power Shot. Remember those over-powered moves you could pull off in Mario Power Tennis that over-complicated a great game and made that great game no fun? Please tell me Nintendo wouldn't be stupid enough to attempt that with Smash Bros...
Now then, my most wanted characters:
Sonic (obviously)
Tails (like Pikachu, I want him there to smash his face in)
Knuckles (an actual fighter)
Amy Rose ('cause there's always a lack of females)
Metal Sonic (or Shadow. Both could be Sonic with different animations, like Capt. Falcon/Ganondorf etc.)
Paula (like Ness, from Earthbound), but with greater Psy-powers!)
Poo (also from EB - for comedy name value alone)
Jeff (see Tails for why)
Baby Bowser (come on, Nintendo! He's great in Double Dash and he'd be great here!)
Balloon Fighter (whose name I can't remember)
Earthworm Jim (I'll get everyone a beer if he's in it)