heh... I still think it's a person behind a mask. Being a god... would draw a lot of parallelism with TRG 2 as Steelfist pointed out, and it's a believable twist to the story. There's all ways the very real possibility that we will simply never know. Perhaps there is a man behind the mask, and then the real Yawah talks to us or something... some clue that keeps the player guessing. Which is likely going to be how it is, as it's one of the main points of TSoG, to explore the existence of god. I doubt Mr. Stern will make such a definitive statement as "there is a god" or "there is no god", as this is a sensitive topic and will likely limit the market of his future games severely.
Though, the "I guess we will never know" endings are all ways horrible. So, I can't wait for Mr. Sterns undoubtedly creative and unique ending to the game.