Takeshi Shudo passed away in 2010, but before that, he was one of the most important writers behind the early seasons of the Pokémon anime series and the first three movies, so his influence on the multimedia franchise cannot be overstated. That said, his thoughts on the conclusion of Ash Ketchum's Pokémon adventure might rub a lot of fans the wrong way, and were they to be considered canon or incorporated into the official storyline, a lot of viewers would likely be upset (via Gamnesia).
Shudo used to maintain a blog, and in 2009, he wrote a post sharing his idea for the end of the series, suggesting that at the conclusion, Ash would wake up as a senile old man, meaning that his adventures, and the concept of battling pocket monsters as a whole, never actually existed. This post was just translated to English for the first time by Reddit user NAveryW, and in it, Shudo writes that Ash just misremembered his childhood, and that the adventures he had and friends he made along the way are filling gaps he experienced in his own life:
Months and years having passed, Satoshi [Ash], who has become an old man, suddenly remembers the old days. It is an embellished memory of childhood. A fantasy...The imaginary creatures, Pokémon, and their adventure. Friendship. Coexistence. That is, in the real human world, something Satoshi could not possibly encounter. However, somewhere in childhood, surely Pikachu and the other Pokémon are there, Musashi and Kojirou are there, Mewtwo is there...
Not just that; everyone Satoshi encountered on his childhood adventure can be seen in the elderly Satoshi's eyes. Satoshi hears his mother's voice in his ear. "Come along, hurry to bed. You set off on your journey in the morning, don't you?" The next morning, woken up by his mother, Satoshi, once again in the form of a young boy, energetically rushes out of the house.
This is a search "Not to catch Pokémon, not a journey to become a Pokémon Master, but to discover what I am", a journey with the goal of coexisting with others.
Anybody with a cursory understanding of the anime knows that this plot development never... developed, and thank goodness, because it would have both stripped all meaning from everything that happened in the show, and it would have been sad as all sadness. It's an interesting thought exercise, but we're glad it stayed at that.
Featured image: The Pokémon Company