Looking at the image, I would have to say that if it is one of the people there, I think it might be The Beyonder. I say this because Bendis, back in the Illuminati mini included an issue where the group encountered him. At the end, after retconning him as a Inhuman Mutant, he goes into dimensional exile. From that mini, this is the only thread that hasn't been picked up again at some point. Molecule Man I could see it being as well. I doubt it's Nate Grey because the entire goal of the Dark X-Men mini is to catch Nate. Regardless, I'm not so much interested and I am vaguely intrigued enough to wait for the trade if I remember.