Mega stones seem like something that wouldn't be tradeable?
If Mega Stones can't be traded but are also version-exclusive, that would destroy every precedent Game Freak's ever set. The only time version exclusives have been unable to be traded is when there's a version-exclusive forme added to a later game, and those get caught up by the next generation. (Deoxys started with only one forme in Ruby and Sapphire).