"Mega evolution unlocks the hidden potential within Pokemon, but Alola is a land brimming with energy, and Mega Stones aren't needed for Pokemon to reach their mega forms here. In fact, in Alola their Mega Forms are their natural forms, found freely in the wild, and their original forms cannot be found in Alola at all."

How would this make you feel? Make all the megas variants specific to Alola like the new Vulpix and Sandshrew, allowing them to keep the new designs and abilities for the megas without having to include Mega Evolution proper.