GF could have planned new megas in SM. Later on, they might have decided to conserve for future games.. It makes a lot of sense. I don't see many megas left for Gen 1-4. Look at Hoenn, the only one they need is Milotic to cover Wallace at something like PWT. I'm sure there will be more Hoenn megas but only few might be remaining. GF is chomping down on popular Kanto mon without megas with Alolan Forms. Ninetales, Raichu, possibly Arcanine and Nidoking.