Whichever event takes place in the next generation, whether it be Pokémon Contests or the Pokéathlon, I think it's possible Ash may take part in at least one of them with the new female member. His goal is to be a Pokémon Master by challenging Gym Leaders and competing in the Pokémon League, but it doesn't halter him from taking part in other competitions either.
Look at his Sinnoh travels, he ended up entering two contests (The Jubilife Contest and the Wallace Cup). He didn't win, but he sure learned some new techniques he managed to pull together in battle. These coming in great use when challenging Fantina. So, yeah, I think Ash just may at least enter one Contest or Pokéathlon event in the next region.