For Gen 8, keep the OU, UU, etc. that limit the Pokemon to the ones only found in Sword/Shield with Dynamax. Call that Standard. Add an additional list that adds all the Pokemon from the previous gens and have its own OU, UU, etc., make only the gigantamax Pokemon able too do so counting as a Mega Evolution, add back the Z-Moves and call it Legacy. Standard would be closer to VGC and the actual game and Legacy is closer to the metagame People wanted on Smogon.