I can't tell if J. J. Abrams is keeping Luke off the radar because of a reveal like this, or if he's doing it just to mess with us and get us to buy more tickets. There was a supposed leak of Luke in costume (which looked like good guy jedi robes) but there is no telling if it's legitimate. Or if it takes place earlier/later in the story.
I definitely don't think he is Kylo Ren. They really seem like they're trying to push the new generation as the core cast, so using Mark Hamill as anything other than a side character/mentor would be surprising. Plus, I feel like making him evil would be a disservice to the character. He managed to overcome the influence of the dark side and redeem his father. To have him swayed AFTER balance was brought to the force, doesn't make any sense. I agree with Titan-Sxull's theory that Kylo and Rey are the offspring of Han and Leia, and will take up opposite sides of Anakin/Luke's legacy.
Also, another bit of evidence is that Kylo Ren doesn't seem to know how to make a lightsaber properly (hence the ragged blade) but Luke already knows how to make a functioning lightsaber.