Feel free to add more responses!! i.e. if there's any Pokémon you think might gain a new Mega Evolution upon the release of Pokémon Legends: Z-A, an upcoming game which is confirmed to have Megas.

If that new Mega Evolution is present on the game's release day (or is announced before then), that option will resolve YES.

(EDIT: To clarify, for a Mega to resolve YES: by the end of Release Day, it must be in the game (either via the base game or a Day-1 patch) OR already officially announced to be coming to the game sometime later. Otherwise, it will resolve NO.)

(EDIT 2: "in the game" primarily refers to "either its 3d model is present, or its Mega Stone is directly obtainable (which implies that it almost certainly WILL be coming)". Learnset and stats (without a visual of the creature) wouldn't be enough. also lol i hate how the "AI summary of creator comment" thing summarized my points wrong, why is it here)

For any "...again" options, that Pokémon would have to receive a NEW additional Mega Evolution (e.g. a hypothetical "Mega Charizard Z", for instance).