It's becoming really obvious that the League is quickly approaching rather then there being a 50 episode gap between the eighth gym and the League. After the League, whether or not Ash stays in Unova or goes somewhere else for the filler arc Trip, Kotetsu, Stephan and Bianca are going to seem really tacked on if they're included. If he stays in Unova for the filler arc continuing their rivalry will seem pointless because there won't be any League battle payoff at the end of the saga. The same gores for if he leaves for another region. If Ash loses to any of them where it counts (the League) people are going to feel jaded if he ends up beating them in an unofficial battle at the end of the filler arc or in some penny-ante tournament.
Burgundy and Georgia may continue to follow Cilan and Iris for revenge, but I can't realistically see any of Ash's rivals being carried over to the filler saga. The same goes for Team Rocket too. They're not chasing after Ash and Pikachu any more so it's going to seem really convenient if they just happen to be going to the same region as Ash after this. It could be okay if Ash stays in Unova though.