Do you believe that the protag is truly Big Boss? Or do you think you play as Solidus? Or perhaps even a completely different clone?
As you well know, the tagline of MGSV is "out of FOX two phantoms were born". I feel like there's a high probability we're playing as the "other phantom" in MGSV and that is going to be part of the game's twist.
Kojima has confirmed that you only play as Big Boss.
Also at the start of the trailer there is a 3rd person on the bed and we see it from his perspective.