I dont think the new villian is Revan. Yes, it would be great, but i believe they will follow a different story arc and i think the new villians will be Lumiya and Jacen Solo. I mean, Lumiya is a cyborg and the new costume looks like a cyborg and obviously, since she corrupted Jacen Solo, the apprentice would have to be him. Plus, Luke is talking to a family member in the trailer bc he says the force is strong with OUR family. So, he is most likely talking to Ben Skywalker. This would mean that Jacen and Jaina exist as well.