How would you feel about companion trainers? Not just an occasional appearance of a rival, but an NPC that spends a considerable amount of time with you on your journey, growing stronger alongside you, and catching their own party of pokemon.
If so, how would you want them to help you during the game? what if their Pokemon knew the HM moves, so that yours didn’t have to. Or maybe, you can battle them for quick exp once a day. Or maybe they’ll heal your pokemon a certain amount of times/day?
Post Stat Trainers.