I've read a thought, and I think it's a good one, that the new style lightsaber the Sith wields is actually a much older one, before the Old Republic, and that the awakening they refer to is an ancient Sith. If we take into account that the prophesy said that there would be one who would bring balance to the Force, that being Anakin, and he killed Palpatine leaving Luke and Anakin: Balance. With Vader dying, and the need for the Force to be balanced, it would mean that there would have to exist a Sith in the universe. Perhaps he's been asleep, or missing from the galaxy, but he's back? Time will tell, I guess, and I'm that much more excited for the whole thing!