The game implies and outright states that the player is not Big Boss. That he's the medic from Ground Zeroes who became big boss. And that the real big boss is watching the events of the game while staging a more covert war against another enemy.
This felt like the biggest Nineteen Eighty Four reference to me. The feeling that the main character has essentially ceased to exist. You have become a representation of something else, of Outer Heaven.
Winston Smith: Does Big Brother even exist?
O'Brien: Of course he exists.
Winston Smith: No, I mean... does he exist like you or me?
O'Brien: You do not exist.
Much like the rest of the series (like MGS2's recurring message of misinformation) MGS5 has a theme of surveillance and loss of identity. And it's open to multiple interpretations as to what that represents.
But that's just my opinion on the matter. I like that the Nineteen Eighty Four references are subtle.