Not to totally buy into the whole "you're not Big Boss" conspiracy theory, but there certainly is a lot of weirdness surrounding the lead. Based on the two trailers we know Big Boss legit goes on Ground Zeroes, returns to Motherbase to find it fucked, and at some point after lands himself in a coma. Cue wake up, assault on the hospital, escape, meeting with Ocelot, and rescuing Kaz.
Based on the footage continuity, we've got two questions.
A) Where does the horn come from? It's not in the post-Ground Zeroes hospital sequence where Big Boss slips into the coma, but it is in his head during the hospital escape (assuming that's it poking through bandages).
B) Who is the man covered in bandages? During the post-Ground Zeroes hospital sequence Kaz identifies a third party ("What about him?"). This person also appears to use Kiefer's voice in the Phantom Pain trailer, though that could be bait and switch. It's not Kaz, that's for sure.
I suppose the weirdness of it all, relative to the conspiracy theory, is the lengths KojiPro is going to make it mysterious. There's no reason to bandage an entire guy's face unless his identity is important, and the existence of the horn is still a mystery.