*Spoiler Alert*
Well, the episode hasn't aired yet, in fact, we are only at the second Hoenn gym episode, which Ash loses.
I somehow think that Ash will have a rematch with Richie or Gary in one of the last episodes. Even though Gary has quit training, I'm sure he's caught new Pokemon to study.
I think the last episode in all is gonna be about Ash finally becoming the champion, a goal that has never ceased since the first few minutes of the first episode.
*End Spoiler Alert*