I have a few ideas that could be implemented to make the league more engaging. And while I would prefer a hard reboot to give newcomers a fair shot, I feel like a compromise could be made.
For instance--we could start over from scratch, but designate some of our old Pokémon to a standby position. We won't be able to use them rightaway, but we won't outright lose them either. After as few months or so, we can use them again.