My thoughts:
- I don't believe on Ash's victory in the Alola league due to the precedents, but i still have a small hope for the future;
- It wasn't fool to believe back then for a victory in the Kalos League, from a "writing standpoint" this lose is still very "illogical"/"contradicting", really, for all the climax enstablised, the greninja arc, etc.
- Writers carried over for too long this old rule (=Ash loser in the end), they are too conservative in many points for apparently no reason (like mythicals, only recently we see some timid changes but for too long for the main characters they are not catchable, and for legendaries... nevermind or even try! most of them for too long exclusive only for movies and only much later, maybe, in the anime, etc.), this rule "worked" in early times but now... after 20+ years...
- I repeat once again, Ash winning a league won't end the anime now, maybe only in the early times (OS seasons essentially). During the DP saga they cleared a bit the matter with the fact that winning a league is only a step towards the (purposely vague) Pokémon Master Dream, and this was reaffirmed some times, for example before the 7th gym match in Kalos. Ash will continue travelling in the end like always, this is a false problem in the end, It would be more or less like after the win of the orange league or even Battle Frontier (shenanigans like: "I always have always something more to learn", "I want to see every new pokemon in the world", "I love random travelling and seeing new regions and discover new things", etc.). But, sadly, for some reasons they don't want to "address" this thing.
So... why still I have some small hope in the (long) future (maybe not for alola league, but probably for the next sagas)?
- After all, there is a (very very sloooooooooooooooooooooooow) ""progression"" in Ash's career in these years/decades, we will still have to see the Alola league but at least in the Kalos league we saw a final for the first time ever;
- Still very late and slowly IMO, but in each new seasons writers start to break more and more old-rurring patters, like recently with the mythicals more often used, the travelling aspect, etc, etc, etc.
So, we shall see (or at least my nephews lol), especially in my opinion if they will start to really use Ash more like a mentor figure for the characters of the relative region (very usually the pokégirls).