Considering Diancie's ability to make gems, the appearance of the Anistar Sundial and its role in finding Mega Stones, and the fact that Diancie is the only Kalos Pokemon to have a Mega, I always thought it would've made more sense for Diancie to be the creator of Mega Stones. It'd certainly be more interesting than the throwaway explanation that they happened to be rocks irradiated by the Ultimate Weapon.
