Since dynamax and gigantamax aren’t coming back, the next gimmick will be something like the spirits from Digimon Frontier. You’ll be able to turn a pokemon into a ‘spirit’ that works like an item that you can equip to other pokemon during battle to raise their stats and/or change their type. Certain pokemon/spirit combinations will trigger a fusion that results in a totally new pokemon.
And because we all know GF is lazy as shit, only a handful of pokemon will actually become a spirit that reflects their species, whereas most of them will become generic spirits based on their type (i.e. charizard will become a ‘charizard spirit’ but other fire types will just become a generic ‘fire spirit’)