Ash needs to win a Pokemon League Championship and one based on the games so the Writers can make a new character and last championship was a total flop and he should have won it
No, he needs to win, and he needs to not be the main character anymore. They can create a more marketable character, if they'd at least try. Yes, they may have to give up Pikachu, or they could give Pikachu to a character that Ash mentored, but that character needs to not be anything like Ash.
If they did it right, and turned it into something more evolved, they'd probably not lose many current viewers, and would bring some back, as well as new people.