If ash beat's Cynthia, after that he'll go and beat Wallace and Lance ( or any other champs if theres any other regions ), then wipe out team galactic, rocket, magma and aqua, then see's ho-oh and battles it and defeats it, therefore it becomes his friend, then it tells of Arceus and how he must defeat it ( a new plot, probably a new seoson ), he'll go on a wild 10-episode search for the Heaven's Pipe, go into Arceus' demension, defeat it, play a sad song and have flashbacks on all of his exciting battles, then the narrator goes: "Ash has finally become the Pokemon Master. But, a new generation comes to pass, a new child from ( any of the beggining towns, littleroot, pallet, etc. ) has had the same dream. Ash's adventure comes to an end, but as a result, a new journey has begun. "
Thats my opinion. =)