>>39275115The problem is the execs have set up rules that Ash isn't allowed to capture any Pokemon that aren't of the current generation unless it's a pre-evolution to a current-gen Pokemon (Forms don't apply here), nor is he allowed to use any of his old Pokemon until Post-League.
GameFreak, being the geniuses they are, decided there didn't need to be any Kalos Pokemon with Megas until ORAS, and then the only Kalos Pokemon to get a Mega was fucking Diancie.
This required TPC to round up everyone to conceptualize Ash-Greninja while the writers came up with the Mega Evolution Specials, since Ash was a long way away from making use of Ash-Greninja at that point and there wouldn't be enough time to shove in all those Megas for him to face.