Ermac, without a doubt. His (their) story was awesomely developed, especially during the post MK4 storyline. I don't see how he wouldn't make the roster in MKX.
I don't care... still think that "fan art" is how Ermac is gonna appear in the new game. The designer obviously had his look for MKX in mind because he went as far as drawing up the hood/mask for each of the 3 variations (labelled v1, v2, v3). If it was just the plain character art I'd be skeptical but the character stance, variation piece makes me think otherwise.
It would be nice to see Smoke too.