It isn't released yet, but I do have a guess.
I think that they will get moves in a similar fashion to how Kyurem-B and Kyurem-W get Freeze Shock and Freeze Burn (or whatever they're called xD), but not whole new moves. Mostly because Mega Evolutions seems to be very much like a form change, and less like an actual evolution. Also, since some of them get a new typing, such as Mega Ampharos, it would make sense if they got a STAB move to go with their new type.
