Considering Sakurai is going towards quality over quantity, we're going to see alot of cuts out of Brawl's roster. 30 characters seems rather perfect for this game. It's a solid and large number. But not overwhelming like something along the lines of say, Marvel vs Capcom 2 or 3.
I don't think we'll be more seeing characters from very much established franchises such as Mario, Zelda, or Kirby. Rather we'll be seeing both characters from other old IPs (Punch Out, Starfy, ect} as well as new 3rd party characters. (Possibly and hopefully Sonic will make a grand return, maybe with Tails or Eggman?) Namco Bandai IS lending a helping hand, so Tekken characters, Soul Calibur characters, and the one and only Pacman are not out of the realm of possibility.