Boon being cagey about the villain.
I suspect Shinnok is involved but perhaps plays a sub-villain like Shao Tsung in MK9 while the big bad could even be a new character.
THe 25 year thing plus the nature of Mortal Kombat's setting make it likely we'll see the return of a fair amount of characters who didn't make it in MK9, though that roster looks quite slim considering there's numerous new characters who won't have been revealed. I just hope Smoke makes it, even if he is Cyber Smoke or whatever.