What they mostly need to do is either fix how Mega Evolution works (regardless of if they ever do GS Cup again) and make Primals count as a Mega.I meant the legendary/primals/megas rulesets. Watch them put Mega/Reversion (and even legendaries) on the same singular option.
Or just remove Megas considering that's easier and I don't know if I trust them to balance them correctly. I think there's really only one Mega that showed the full capabilities of the Mega Evolution system which is really unfortunate.