But we don't actually know whether or not Ash will retire from the original main anime and then become replaced by our new main protagonist boy or girl Pokémon Trainer heroine right after the Pocket Monsters 2019 new series (known in the international dub as the Journeys series), or will he return in the next series based on main series video games or instead set in the alternate continuity in the original main anime. But we'll see. Thanks. :)
No, we don't know definitively yet. I'm just speculating based off of my observations. In 20 years, Ash has arguably never had a more OP team,
maybe his Kalos team could rival his current one but, who knows for sure. By introducing Goh I
personally think that the writers/creators are testing the waters with the fans to see whether a new protagonist will work or not going forward and what better way to send Ash off than by winning the Pokémon World Championships.