If there's one thing we know about Charles Xavier from the future (or our present, I don't even know anymore), it's that he is shorn of the long flowing locks sported by James McAvoy in the previous two X-Men films. This movie will see the the big change in appearance finally happen, and we've already seen a picture of McAvoy having his head shaved. He won't be starting the film bald, but it's going to happen at some point, thus completing his transformation into Professor X. Since we've already seen it, and the prospect of a bald professor in action is definitely something enticing, then some footage in the trailer would make sense. Using Cerebro, the chair spins round, and there he is, hair-free.