No, Ash Ketchum should not be replaced from the Pokemon Animation series because he is the main character of Pokemon, and Pikachu is his best friend. I would think that if someone else was the main character, then Pikachu would hate him/her. No one likes a hating Pikachu around the show.
I mean seriously ash is so old that it's not even fun to watch any more. All he does is pull out pikachue and wins almost immediately is not like the real game where you lose and win. Ash's Pokemon don't even level up at all and he has like level one Pokemon.
Sure Ash is for some reason ageless so no matter how many episodes he goes through he never ages. But that doesn't mean he should be removed altogether. The origin story of the friendship of Ash and Pikachu is too heart warming to ignore. Red also never ages but he has no history as far as I know (Let me know in the comments if that is true, I'm not a fan of the games)