Now that we have possible bios for Sonya, Jax & Kitana, we can assume that they have a high chance for being super unlockables. Who do you think is closest (not who you'd like) to being one? NOTE: Put facts why.
I say:
Drahmin: He's in the prison stage & mentioned as a foe to Scorpion.
Frost: Mentioned as an ally to Sub-Zero.
Shang Tsung: mentioned as an ally to Mileena.
Kung Lao: Mentioned as an ally to Raiden.
Sareena & Mavado: Had budding stories in MKDA/TE, that could have long term effects on the MKD story.
Quan Chi: He's seen in fighting Scorpion in chess kombat, but we don't know if the video is outdated or not.
Rain: Every Edenian & Ninja are in the game, why not?
Sektor: see Sareena & Mavado.
Reptile: Based on his ending, we could see him in it.
Shao Kahn: He's mentioned in several bios, so maybe...
Cyrax: Some say he's Darrius, some not. We may never find out...

As for the ones that won't be in it:
Cage: No storyline whatsoever. Kobra's here to stay.
Hsu Hao: He's pushing daisies.
Blaze: He's got nothing to do.
MoKap: Joke kharacter & nothing more.
Nitara: stuck in her vampire realm. Doubt she's there.