Have an elimination tournament with your opponents randomly chosen (hell, they could even be selected from different real-world players that are connected via wifi when THEY fight the league as well, but computer controlled). Level could be within a certain range for each "round," with the ability to rest up between "rounds (which could be after a few trainers)." IDK how many rounds there would be.
Or just make it a 16 or 32 round elimination tournament, or modified tournament. -first few trainer battles are 3v3 (qualifying rounds) -later it's 6v6 (imagine it like the Sweet 16 or Elite 8 from the NCAA tournament).
Scenarios like this would be more interesting IMO. The whole E4 as part of the story doesn't do it for me anymore. Not enough to keep me from buying and playing, but it's kinda old.
You already have the PWT, why would you want that?
The PWT trainers are awful. Just sayin'.
The Champions are awful.
Lance's team is somehow even worse with all Dragons, including lolspecialFlygon. Steven replaced Skarmory with Archeops (!) and has all physical attacks because no Claydol (just burn them or use a physical wall to win). Cynthia doesn't have bulky Milotic or Gastrodon - lolGlaceon. Blue has no Tyranitar so nobody has autoweather.
Shell Smash Cloyster can solo nearly all of them. Sash it, give it Rock Blast, Icicle Spear and HP Ground (for 'Gross). CounterBond Gengar is amazing too.