Wouldn't it be cool if there was some kind of Pokémon loyalty system built in? I don't mean affection, but a chart that catalogues your wins, losses, number of summons, items used, etc. If you reach a certain point with your chosen Pokébro(s), they get bonus stats (perhaps IV increases) and special moves and abilities that they wouldn't otherwise have?

This could be a good way to make certain Pokémon competitive when they otherwise wouldn't be (and make others even more OP when they already are).