>>58737250the ability to use gimmick forms like megas or gigantamaxes is fundamentally tied to being unable to evolve, evidenced by the fact that gmax factor pikachu, meowth, etc. cannot evolve, are not affected by eviolite, and cannot be transferred out of home to games after sword/shield because those games don't keep track of the gmax factor and thus would introduce inconsistencies with those pokemon being allowed to evolve in, say, SV
however these pokemon can be freely made capable of evolution again whenever you want by feeding them max soup to remove the gmax factor, so this state of evolutionary lock and temporary form access is not permanent and can be adjusted on a case-by-case basis
this doesn't only apply to gigantamax though, because like you said eternal floette is explicitly only capable of mega evolution due to being barred from regular evolution, meaning mega evolution operates under the same ruleset
so it's very explicit that only pokemon that cannot evolve for whatever reason are capable of attaining these temporary form changes
all a new game needs to do is introduce the idea of a "mega evolution factor" and then it's completely congruent with current lore and new evolutions can be added for pokemon that have mega evolutions at present
now eternal floette is just a floette permanently stuck with the mega factor, and you can just feed your mawile some mega soup and boom you can get a mawmawile
