Storyline-wise who we COULD see return based on the charcters we see in the trailer, mind you this is not a: I WOULD like to see return.

Sub-Zero:
This is beside the point wether it is Old or new Sub, or if he turned evil by the Medallion.This is just a Summery of people invovled within Both Sub's Storyline: Smoke,Sektor,Frost,Sareena,Scorpion,Old Sub-Zero.

Scorpion:
Pretty sure he has a vendetta with some people:
Quan-Chi - Drahmin,Moloch,Old Sub-Zero.

Mileena:
Last time she was resurected it was by Shinnok,so it could be she was still working for him, yet this is irrelevent,as stated above.We could see return:
Noob Saibot,Kitana,Queen Sindel,Shinnok.

Baraka:
Pretty steady ally to Shao Kahn if you ask me.
We could see return:
Shao Kahn.

As for the *new* roster we saw in the trailer:
Ermac/Kenshi/Belokk/That guy with big red trousers: Wether or if this is Emrac/Kenshi, I don't know, could very well be a NEW charchter, ever thought of that?

WHite female Raiden look-a-like, and the guy she was fighting: I am not going to even go there a bit to vague for my liking.