As far as the various franchises go.
If another Expanded Marioverse character appears, it will be Diddy Kong, Baby Bowser, and K. Rool in that order. Yes, we do not have Toad yet of the Mario Sports 8, but what does Toad really do in the Mario games? He does nothing for the most part. Hell, he was only the hero in two games... Super Mario Bros. 2 where he shared playability with Mario, Luigi, and Peach... And Wario's Woods, where Toad didn't even get top billing. Toad's not essential to the Mario games. Mario & Luigi are the heroes, Bowser is the villian, and Peach is who you have to rescue. DK, Yoshi, and Wario meanwhile are representing their OWN series instead of Mario's. The other two, Daisy and Waluigi, are not possible as A) Daisy snuck into Melee as Peach's alternate outfit, and B) Wario is representing WarioWare, not Wario Land. Waluigi has never appeared in a WarioWare game, so he would be mismatched with his brother. Diddy Kong is DK's sidekick, and K. Rool is DK's villian, which makes them representative of the Donkey Kong Country series. Now Baby Bowser... Why him instead of Bowser Jr? Well, basically, Baby Bowser and Bowser Jr. have the same **** design and VA now... I'd imagine the fighter to be an amalgamation of the two. Baby Bowser gets the nod however, because then he gets to represent the Yoshi Series as the main villian.
Kirby needs Dedede playable, nuff said.
Zelda... Only Link, Zelda, and Ganondorf are important characters to the Zelda Series as a whole. I know you guys want Midna, and Skull Kid, and Vaati, and Error, but we'll be lucky to get a Wind Waker'd Young Link.
Pokemon... Well, Pikachu's the mascot and Mewtwo is the Pokemon that is best described as the final boss... Being the End Boss Pokemon of four games (Pokemon Red/Blue/Yellow, Pokemon FireRed/LeafGreen, Pokemon Stadium 1 & 2). Jigglypuff has her fans, and my guess is that Lucario (Best Representative of Diamond & Pearl) will replace Pichu, not Mewtwo.
Starfox... I guess Fox and Falco will return with their movesets from Melee, except they will have different Final Smashes... Of the next choices for a Starfox character, Krystal is really the best choice, because of her staff from Adventures. It gives her an original moveset over Wolf, who would be the next choice and who I can see being a villian in Story Mode and being a remodel with Fox's moves.
Golden Sun ought to have a representative in Brawl, and Isaac, being the first hero of Golden Sun, is a good choice... Plus, if we are going to have another swordfighter, he should have a totally different moveset from Link, Marth, Pit or Metaknight.
Mega Man and Simon Belmont are always good choices to be in a game featuring Kid Icarus. However, there is more of a chance of Phoenix Wright being an Assist Trophy, than Viewtiful Joe has of being in the game... Joe really got snubbed from the SNK vs. Capcom Card game for DS in favor of Onimusha, Devil May Cry, and Phoenix Wright.
Of course, my out of left field choices are Mac from Punch-Out!!, Takamaru the hero from that obscure Famicom Disk System game that keeps on being considered in the same group as Zelda, Metroid, and Kid Icarus, Lolo from Adventures of Lolo, and Balloon Fighter. Also Ice Climbers, and Mr. Game & Watch will stay.