I think eleven newcomers is a BIT low. And that's including Mewtwo. Besides Waluigi, the choices aren't BAD. Maybe a tad... expected, which is boring, imo at least.
Here's my 20 possible newcomers but the characters with my comments are always the divisive choices.
Balloon Fighter - Sakurai inadvertently debunked the "useless without X" excuse when he added Olimar and he still could change his mind
Captain N - a non-video game character with history with Nintendo? A good WTF choice.
Chrom - he is most likely getting in whether he is replacing Ike or keeping Roy out
Dixie Kong - she's still a possibility given her data in Brawl
Impa - it is possible Sakurai could, you know, replace Sheik with Impa if he wanted to
King K. Rool
Little Mac
Mega Man
Mii
Pac-Man - he is the obvious rep for Namco but other people want a Tales or Tekken character
Palutena
Pokemon Trainer Gold - didn't someone translate Sakurai's pre-Melee comments about wanting to add the Johto trainer as a 2nd gen rep?
Ridley
Shulk
Takamaru
Toad - a popular Mario character who recently gained prominence and moveset potential from New Super Mario Bros. Wii + U
Toon Zelda - she's still a strong candidate given her data in Brawl AND Wind Waker is getting a HD remake
Villager - again, Sakurai could change his mind and he knows Animal Crossing is pretty damn popular for a non-violent game series
Waddle Dee - Sakurai could be biased and add him if he wanted to
Zoroark - this Pokemon is still an option if Sakurai decides to add a new Pokemon from the latest games