Ideally, there won't be another "reset", but rather just an ending.
Honestly, if they really want to keep Ash, then just write an ending to current Ash's story. Then they can do a complete restart with Ash/Pikachu in Gen 9's region.
Well, if the writers did end Ash's story in DP based on everything they set up, then the anime would have finished at 660 episodes. Still very long, but better than the 1070 we're at right now. The problem with the anime is that it's episodic and repetitive (especially with Team Rocket) and has plenty of fillers, so I'd say a couple hundred non-essential episodes could be removed right there.
I think it's realistic for a trainer to take time to become good. Perhaps AG Ash should have showed up in Johto, and each region's development could have been bumped up a region. Other than that, I thought OS --> DP was fine. The opposite extreme happened with Sawyer in XY. He shows up as a rookie and gets demolished by Clemont, Valerie, and Ash. Then 60 episodes later, he becomes some Smogon analyst with a fully evolved team. It was jarring.
XY showed Ash and Alain faring well against the Elite 4 and Champions. Ash already completed the Battle Frontier, and some of the Frontier Brains are on par with the Elite 4. On top of that, Pikachu, Charizard, and Sceptile defeated legendary Pokemon. I think with a DP or XY competency + his best team (Pikachu, Charizard, Greninja, Sceptile, Infernape, Snorlax), Ash definitely could take on the Elite 4.