We can't stress this enough, there are SO MANY CHARACTERS in X-Men: Days Of Future Past. As well as reuniting with old / young versions of all of our friends, we get glimpses of Blink, Sunspot, Bishop and Warpath.
How on earth are they going to fit them in? Omar Sy is a brilliant actor, and Bishop is a fan-favourite character, so we doubt he's been cast for a cameo.
Perhaps he'll be introduced, and saved for a more major role in the sequel, which we've got a theory about. But we'll get to that in a minute.