Needless to say while im frustrated with his lack of more concrete development as anyone else i don't want him gone just to end up with replica of current character still suffering from lack of substantial growth, being reset at start of every new saga and having more or less similar quest collecting badges, personality, and storyline like Ash currently does.
Because with current limitations and writers lack of motivation to jump hurdle and take anime to higher level nothing would have changed for better with new protagonist.
Considering how issue doesn't lie in Ash character and lack of potential which clearly is there to be done more, but writers and as long they don't decide to break mold and add new , different spins to anime and characters no amount of new additions is going to change current formula.
Moreover if your going to make replica of Ash with new guy using Pikachu, might as well keep current protagonist instead.
Large appeal behind this show comes from being treated as entity based story which is set in same timeline and universe exploring on constant protagonist and his companions supposing to follow them on adventure and receive build up on stories and friendship as they get to know each other over time and share their ambitions and dreams.
Making pokemon unique and different compared to other anime adaptations which usually last for 52 episodes being chopped in multiple alternate deviations.
Personally i would rather want that writers for change invest more in Ash story take established character to new, unexpected directions having more complex growth. He hasn't won a league yet,concept of champion league which was for first time brought in DP has been relatively unexplored and Ash never officially challenged E4 and champion so there certainly exist prerequisite to do follow up of what what developed in past.