So its like this, what if with this holiday release GF gives us some "presents" with this feature.
- Activating Bank unlocks more mega stones. - Transferring a certain number of unobtainables unlocks even more stones. - Transferring Event Pokemon (eg. shiny creation trio) unlocks XY Events. - Totally completing your dex unlocks legendary mega stones, or even one of the rumoured Diancie & co.