>>47164734I had an idea similar to that for a region without a central evil team. Your rival would be all wide-eyed and friendly with you since you're best friends, but would increasingly get more frustrated and self-loathing at your progress compared to his(imagined) lack of it, like Calem/Serena does but much more serious.
It'd basically end with him releasing all of his mons and a kind of search/reunion where his ace mon would ask for your help in collecting all of his released mons and making the rival see the light.
The true end of the arc would be something like
your rematch against the E4, and finding he's replaced the oldest member that was ready to retire but wanted one last grand finale before leaving. Or something like that.