Yes, Ash needs to retire. We've (in my own opinion) sucked all the potential out of him, and he did his job well. Over the years he has made Pokemon fun and funny. I really think though they should move on. Sorry. Pikachu, eyyeee, this is tough. If they replaced him, people wouldn't like the new central protagonist having "Ash's pikachu". Hmm... I don't really want to make a "therefore" kind of statement about this and regret it later.
Maybe they should just take a break from Ash like they did in Chronicles. Or, have a new main character and make Ash reappear every so often as a friend of the protagonist.
As a huge fan of the Chronicles series, I would love to see a Chronicles 2. And as an admirer of Pokemon Chronicles I wouldn't mind if Kenta did a swap with Ash. He's the better Ash in my opinion.
I guess what i'm saying is I think Kenta/Jimmy or another trainer would make a good Ash for a while with Ash reappearing every so often. The least they could do is take a small break from Ash for a while, but I doubt any of this will ever happen, unfortunately.