You may also notice that Revan has a completely different voice actor from when he appeared in earlier content in the game, such as the Foundry/ Maelstrom Prison flashpoint arcs. It's tough to say whether this was intentional foreshadowing on Bioware's part or whether or not it was just due to a staffing change, since they played a similar trick with the Dread Masters that was obviously intentional.
If you pay attention, you'll notice the Dread Masters had two distinct voice actors for each of them, one of them is used when they communicate telepathically with you, and the other is used when they speak in person, this foreshadows/implies that the Dread Masters were actually separate entities from the physical people that we killed in Dread Palace, which is basically confirmed by Calphayus in the conclusion of the Republic story arc, where he surrenders to you, confused and terrified, and talks about how they basically became a separate entity when they put on the masks, strongly implying that they had been possessed by much older entities.
Warning, MAJOR spoilers follow for two of the class story arcs in SWTOR
We know for a fact that Vitiate is not dead, the Jedi Knight kills the Emperor's Voice on Dromund Kaas, but a post chapter 3 quest with Kira and some of the other Children of the Emperor strongly implies that, while we killed his physical body, his spirit was not destroyed, just greatly weakened. Furthermore, the Emperor's Wrath receives a mail after the conclusion of their Chapter 3 story arc from the Emperor's Hand themselves that directly states the Emperor is not actually dead, and is instead recovering for his eventual return, in a secret location, telling them to tell nobody of this.
Several of the post- class story story arcs have hints that they were engineered by Vitiate in order to distract the galaxy from him and keep them from digging further into the circumstances of his supposed death, particularly the Dread Masters, who are broken out of Belsavis prison by the Imperial PCs by the order of the Emperor himself, and yet later go rogue. Given that Vitiate has shown himself to be an insanely gifted chessmaster who plans for virtually any possible contingency, I doubt this is a coincidence.
Anyway, it's tough to say at this point, but I basically believe that either it really is Revan, twisted in some way, and possibly by the Emperor himself, or even the Emperor himself returned to life in the guise of Revan. This would play directly into his hands, since the Revanites were stated to believe that Revan had secretly overthrown the Emperor and ruled in his stead for many years, which would give him the authority to command them.
Regardless of which is true, though, Revan has clearly had a dramatic personality change since he last appeared, since he had basically been driven insane by 300 years of direct mental contact with an entity who can no longer be said to be a person, aka the Sith Emperor. That raises the question of whether or not what we are seeing now is Revan's true personality, recovered from insanity, or whether or not he has been driven deeper into madness by whatever happened to him after his supposed "death".