RileyXY1
Young Battle Trainer
I don't think that Ash will not compete in the league.Alternatively, what if something happens to Ash and another trainer has fill in for him? It would explain the minimal Pokemon teams since putting Ash's with one of the others could make a full six. It would also sneakily maintain his top form from Kalos.
I could see them maybe asspulling the '11 years old to enter' mandate from the games (did Kukui ever find out Ash's infamous age?).