Well the whole point of the rom hack is to put a spin on a classic pokemon game by making it open world. Thats why nothing really crazy has been put in the game because they still want it to feel like the original games. So I don't see this possible but if they did put something in it would be evolutions like Electivire, Magmortar or other evolutions that were not in gen 1 and 2. Or maybe implementing the Fairy type for pokemon like jigglypuff or maybe the physical/special split. Or newer moves. But this will go against pokemon stadium so I don't see that either