so, assuming gamefreak (or any fanmade game creator) took on the undertaking of introducing this concept, how would they limit it, and what would the mechanics be? i'd imagine the offspring would be of the mother's species with the compatible father's addition (so all of the crossbreeds in pic related would have a slurpuff mother). would most likely be limited by primary egg group, and probably also type (and maybe just choosing not to do certain variants). also, crossbreeds would be able to breed, but the offspring would have the same base mechanics (so a male pikachu and a female marill-breed slurpuff would just make a pikachu-breed swirlix).

ditto would obviously be excluded from this, as otherwise you'd just have a bunch of goo crossbreeds, or crossbreeds with ditto face, as hilarious as that would be. also genderless pokemon obvsly wouldn't be able to do this.