pablumatic said:

Hmmm. The photo of Kylo Ren/Adam Driver in costume without a cyborg head seems to point more towards the speculation that the cyborg-headed guy holding Vader's mask in the production photo leaks is Luke.

Well Hamill said he grew out a "contractually obligated" beard, which could be a joke but he was sporting one for all of filming. It doesn't make sense that he'd go full cyborg and lose everything that makes him identifiable as a character.

Provided Abrams' version of the Sith go by the master and apprentice rule, perhaps cyborg dude is the master.