If the anime goes that route and decides not to pull the trigger (make him a Master) then the entire series never lived up to anything. Maybe that mini-clip is just a tease to play on our expectations, but for the generation that grew up watching this adventure about a boy on a journey to accomplish his dream only to be told that its impossible, makes 26 years of support meaningless.
Based on how Pokemon Master is being interpreted going off the possible leak given from Yuyuma's interview about the goal/ dream being somewhat untouchable like a rainbow, is as if making Ash a Master would be equivalent to him being some type of demi-god.
Sometimes I wish this anime would use more ideas or concepts of inspired from different anime's, like how dragon ball handled Goku's ascension to Mastered Ultra Instinct, by establishing that the just because a character takes on the role of being a master at what their taught does not mean they've reached peak perfection to be incapable of learning new things, thus their journey continues.
He's already a Pokémon Master. I've been keeping track of him from beginning to end, noting how Ash has changed over the course of 26 years. From Newbie to Learner to Experienced to Junior Mentor to Advanced Battler to Competitor to Experimenter to Ace to Graduate to World Champion, Ash has become the very best like no one ever was.
But what fun is there to be at the top with no challenges left? What is there to life when everything is accomplished? There should be something more for Ash. A new region to explore. A new Pokémon to find. To make new friends and walk to the next city. To find new challenges to pushes you to your limits. To learn and experience new things this world has to offer.
What was it that I said about a Pokémon Master?
Ah yes... To be a Master, A Pokémon Master, is not a goal. It's a drive that keeps us going to improve ourselves.
The funny thing is... I learned this lesson when I watched a video back around 2018-2019 that claims that Goku wants to have opponents stronger than him so he can always strive to better himself as a fighter and person.