Wario, if he returns, is the only "evil clone" esque character notable enough to get their own slot. No other dark counter parts have made it to separate character status in the world of Smash.
Dark Link, probably a costume again.
Toon Dark Link, made up in Brawl, probably a costume again, prefer the Lobster Shirt Link...
Dark Pit, made up in Brawl, likely a costume again.
Blood Falcon, likely a costume again.
Dark Samus, assist.
Waluigi, assist.
Shadow, assist.
Unless you count Wolf.. if he returns.
Mewtwo wouldn't count since Mew isn't playable.. lol
I think they should reveal Wario, Ganondorf (new moveset), and Game & Watch since they kind of did, and they reveal a bunch of alternate costume characters (ushered in by Pittoo and Wario); Pittoo, Dr Mario/Jumpman, Mr L, Shadow Queen/ Daisy, Dry Bowser, Wario's alt, Dixie Kong, Dark Link, Lucina (Marth), Chrom (Ike), Louie/Alph/etc, Ms Pacman, maybe Birdo, maybe Impa, etc. Although they could also reveal Ness, and then announce that due to custom movesets that Lucas and Falco will be alternate costumes for Ness and Fox, or do a "just kidding" and show them completely revamped and different from their parents in the cloning process.
I guess I predict Game & Watch to either be officially revealed as a POTD or completely ignored, and then some villains and or alternate costumes to be revealed. New Ganon(dorf), Wario and maybe Wolf, maybe a newcomer villain (Ridley or KK Rool, or Vaati to rival Toon Link and accompany Ganondorf), and then they address clones being dissolved into costume swaps, which would explain Dark Pit, could be addressed as Dark Pit or Pittoo, but shares a slot and entire moveset with Pit, much like the Wii Fit Trainers and Villagers do. Would be interesting. We'll probably get nothing.