oh man i've had this 'episode' idea in my head for ages xD.
i totally think it'd end as the last 10 minutes of the final pokemon episode. they fastf orward 10 years into the future (so ash would be like 26, idk) and you see Prof Oak handing him an award on a stage proclaiming he had finally reached his goal of Pokémon master and he's about to make a speech when two kids, a boy with black hair/green eyes, runs on stage proclaiming he's gonna be pokemon masters one day too. Ash would laugh and Prof Oak would say something like "And let the new generation of pokemon begin!" and then a happy pan across the crowds zooming in on important characters.
the final scene would have ash, misty, pikachu, his mom, prof oak and the kid on stage smiling proudly. ^u^