New Mega Evolutions. None of which were hidden in the games' coding. If there were placeholders, we never knew about them.
There can still be more Mega Evolutions.
Other Pokemon still have a chance to score big with Mega Evolution. (I'm crossing my fingers for Honchkrow, Hydreigon, and Sableye now. Of those three, I find Sableye and Hydreigon very likely. I just hope that Honchkrow isn't just wishful thinking on my part.)