Pokémon Journeys may be a good excuse for the writers to include the playable characters (other than the ones already in the series like Dawn, May and Serena) in the series. In Journeys, Ash and Goh travel to other regions and learn more about different Pokémon, battling other trainers, catching new Pokémon and etc. Perhaps Ash and Goh could run into the playable characters (Brendan, Calem, Victor, Elio and etc.) while traveling to those regions, befriending them, battling with them and etc. Some playable characters like Brendan, Lucas and Ethan have made appearances in the movies, but they are only minor appearances and not for that long (at most a few seconds). The writers should’ve written them in already, at least as one of Ash’s companions on his journey. Adding them in Journeys could/would remedy this.