They tend to put to promote Ash's Pikachu vs Leon's Charizard in this Generation. But honestly, since Ash's main rival this season has a Charizard, I believe it should be a good chance to bring back Ash's Squirtle, make it evolve to Blastoise and have a new version of Charizard vs Blastoise, but with Ash on the other side.
By the way, if they use the Isle of Armor's plot, I believe Ash could get Kubfu and evolve it into the Single Strike version; because it matchs his personality better. In the case of Mustard, he suits the Rapid Strike better because of his experience. Another clue for Ash's Squirtle to return and evolve would be Honey having Venusaur Gigantamax, because the Grass Type would be useful for Honey to get Max Mushrooms.
By the way, if they use the Isle of Armor's plot, I believe Ash could get Kubfu and evolve it into the Single Strike version; because it matchs his personality better. In the case of Mustard, he suits the Rapid Strike better because of his experience. Another clue for Ash's Squirtle to return and evolve would be Honey having Venusaur Gigantamax, because the Grass Type would be useful for Honey to get Max Mushrooms.