Where is the rumor for Pac-Man and Little Mac to be revealed before the end of E3 coming from? That would be cool. I don't know how/what they would do with the Mii though, move-wise.
As for characters I think should be included/want to see:
Wart - Complete with Bubble/minion/magic attacks.
Captain Maple Syrup - Another female and villain character.
Little Mac - Duh. Obvious choice.
Chibi Robo - If they could make Captain Olimar and the Pikmin work, they could make Chibi work.
Simon Belmont - Similar to Mega Man, have him inspired by his NES appearance, with an awesome CV stage.
Pac-Man - Why not? Classic gaming mascot. ONLY Namco character I would really want to see included.
Bomberman - Would be awesome, but I think Hudson Soft is sadly dead. Stupid Konami......
GANON - Instead of Ganondorf, why not have the classic, WIZARD form of Ganon, with trident?
Mach Rider - Not sure how they would make it work, but I could see it. Would be odd/awesome.
Mike Jones - From Star Tropics, complete with ST stage and his Yo-Yo attacks. Really want.
Dixie Kong - Another girl character, and she could have unique hair-based attacks.
Characters I want to return:
Basically everybody from Brawl, except for Snake. And I suppose Ike would be replaced by a new FE character that hopefully plays the same, because I liked Ike's moveset. Hopefully no more clone characters, so it would be nice to see Falco/Star Wolf their own final smash moves. If one of them has to go, make it Falco, because Wolf is awesome. I could do without Toon Link, though he did have a nice moveset.
Characters I DON'T want to see:
Basically any needless 3rd party character. The game doesn't need to be stuffed with 3rd party inclusions just to make every fanboy happy. At some point it stops being Smash. The series is, at heart, a celebration of Nintendo.
I really don't want to see Bayonetta, because she just doesn't fit. A "mature" type character like that, especially her, really doesn't fit the Smash style or universe. Just because Nintendo is publishing her second game, doesn't mean she needs to be included.