Basically, Gen VII will see cross-generation players (with cross-generation breeders being a sub-set) playing a very unique role: they're basically going to introduce the old pokemon into the new "meta-environment" (which includes both the competitive "meta-game" which is determined by what is natively desirable and is one subset of the meta-environment, and also the native environment, that which is natively available to the Sun/Moon cartridges and is also a subset of the meta-environment).
