So I'm bored, let's look at all characters without "clones" (as much as I hate the term). I'm totally OK with most of these characters getting someone to play like them.
Peach
Bowser
Wario
Donkey
Diddy
Yoshi
Zelda
Sheik
Samus
Pit
ROB
Ice Climbers
Kirby
Meta Knight
DDD
Olimar
Pikachu
Zard
Ivy
Squirtle
Jiggs
Lucario
Mewtwo
Ike
Sonic
Snake
G&W
Wolf *
*Not a clone, but I REALLY doubt anyone wants another spacey.
Whew... so there's a lot of characters who have potential for unique interpretations of their moveset through another character.
IIRC, the hype for Sami was due to a quick Snake clone being possible.
Idea dump:
Peach - Daisy?
Bowser - Bowser Jr. (If he's not unique)
Wario - No one else can really inherit his moveset without being Wario.
Donkey - Funky or another Kong.
Diddy - Dixie or Tiny.
Yoshi - Birdo?
Zelda - Toon Zelda
Sheik - Impa (Probably not in Brawl) or Tetra
Samus - Dark Samus (sorta)
Pit - ???
ROB - ???
Ice Climbers - Pichu Bros. or Pra_Mai
Kirby - Can't really clone Kirby.
Meta Knight - Galacta Knight (Not in Brawl?)
DDD - Maybe K. Rool?
Olimar - Louie
Pikachu - Pichu or Raichu
Zard - Charmander or Charmeleon (Difficult due to lack of wings. Maybe Ridley?)
Ivy - Bulbasaur...
I MEAN VENASAUR! (egoraptor ftw)
Squirtle - Wartortle or Blastoise
Jiggs - Igglybuff (even more polar lol) or Wigglytuff
Lucario - Another fighting Pokemon?
Mewtwo - Mew?
Ike - Hector
Sonic - Other, similar Sonics
Snake - Jeff from EB, Sami/Andy
G&W - Paper Mario (if that isn't a stretch)