>>36933684Eevee already has the Evoboost Z-Move and would probably not get new moves; +100 BST doesn't do much for it either.
Seperate mega for each Eeveelution would be preferable, they could all use the same stone though. 625 BST is also very nice and they could easily be min-maxed to Ultra Beast levels.
Mega Eevee has a higher chance of happening because having 8 Eeveelutions + 8 Megas would be an over saturation of merchandise 