When the Anime of Pokémon was still new, the man behind the scripts was Takeshi Shudo (Martian Succesor Nadesico,GoShogun, etc). He was the man in charge from the series beginning to the Johto arcs, writting also the first 3 movies. Well, it seems he already had an idea in how the anime of Pokémon should end.
While the comment about this topic on his personal blog it is not new, this is the first time that such information has been translated. Here it is such comment:
“Months and years having passed, Satoshi, 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.”
It is obvious that such plan was never used due to the big popularity of the show alongside the games and the other merchandise based on the Pocket Monsters, making that new seasons where greenlighted; but in any case, would you have liked that ending?