You all remember back in Advance gen... during the Battle Frontier series? When Ash was controlled by the evil spirit king? And then no one could snap Ash out of it, but then Brandon reminded Ash that he has friends??
Well... Back in the Malmar (I probably spelt that wrong!)... Malmar said that he would come back and control everyone, because that was his plan... and what If that happens to Ash later on? For say that everyone tries to get Ash to return to normal, but fails. Except for Serena. Serena would be the one to get through Ash and get to his conscious by reminding him of their childhood or something. Then that snaps Ash out of it all, because of it all, Ash then realizes he has feelings for her (OKAY maybe that part would still take a little time to work on... lol)
So.. yeah... that was the thought that was tinkering around in my head hahaha
I have a more interesting crazy theory (and gomen kudasai if it's tl;dr
and if it's more like plagiarism of the Goku vs Majin Vegeta fray on DBZ...)
For tl;dr
-Satoshi goes on a losing streak against certain recurrent rival and gym matches, gets on a brooding state (AKA the Hikari Depression arc rewritten on Satoshi) and TF gets an opportunity not to hypnosis him... but to possess his body, mind and his pokemons after realizing 2 things... 1) They've failed with the first mind control in ep. 19 and 2) Flare Dan realized Satoshi has insecurity issues and a glimpse of an evil side (aka Pokelantis) inside his body. They succeeds on possess his body, mind and his pokemons (nothing to say... Satoshi left them to do that cuz he was in a brooding state). Satoshi returns to his Kanto personality, but with his impulsiveness, arrogance, stubborness, obsession and pride "up to eleven" and becomes more aggressive and prone to anger outbursts and retaining his competence. His Pokemon would become stronger than before because of said possession. The only thing Flare failed to fully possess... his desire to become Pokemon Master, his trainer's pride and his loyalty to his friends).
-Said recurrent rival reappears and a barely possessed "Majin-Satoshi" blackmails him to provoke the rival in order to get a full battle 6 vs 6 rematch after the Kanto-boy disobeys a TF's order to attack his friends (yeah, his good side wasn't wept out at all. He only left TF possess him cuz he wanted to rematch that person).
-The fight goes and the rival questions him about his methods and Satoshi admits his way was very humilliating for a trainer who relies on hard training and fighting spirit, but he hadn't option in order to regain his impulse to become Kalos champion and get nearer to his dream (with some "about to fistfight" but nothing more than that).
-His friends beg him to stop without results after they realize the fight went too far cruel. Howevuh, Serena success on get him to stop (more or less similar to the scenario you've posted).
-The rival, despite the way the fight went, gets impressed about Satoshi's desire to win and become Kalos Champion, and grants him a more equal rematch... but in Kalos League.
After that Satoshi's Pokemon would retain his majin induced abilities (and some ones would be able to mega shinka), but he would be more jaded and aloof with his human friends than before after realizing the psychological damage he's done to the people around. Also his friends (and specially Serena, whom Satoshi would become more tsundere with, cuz he realized he has some feelings after the "stopping the fight plea") would be more concerned about his aloofness until some episodes later.
Here's a fun topic I saw being brought up else ware, and could bring up some a fun scenario:
How would Serena react to Bonnie targeting another girl, to ask to marry Ash.
Aaaajajaajajajaajaajajaaja. Serena (and Satoshi also) would be totally freaked the hell out, and suddenly would burst out into a "Mind your own business Eureka! Satoshi is busy training hard to reach his dream!! He hasn't the time to think about that things right now" (yeah! I would figure that would be the outcome. Serena had shown to be concerned about Satoshi's dream as well).
Could it be possible, that Pokemon XY will be the last Pokemon Chapter? It would end at episode 1000, which would be a great ending.
As Ash would become the Pokemon Champion, he could finish being completely focused on Pokemon and could start focusing on real life with Serena^^
Pokeani isn't likely to end... but there are high chances to be retooled on Gen VII because certain popularity on children issues. Neverthless if that retooling implies Satoshi being written out, it's highly implied he would be written out with Serena.
However if Satoshi continues in Gen VII, there's ALSO high chances he would be written out next gen (but there the chances to be written out with one of his past female companions, not only Serena, would be high). Game Freak admitted on the last Q&A session on Twitter they want to make the next game with all regions and they are inducing the fans to send them the most interesting ideas to make that happen.
About ep. 1000... i don't want to make predictions about that.
