No way, Pokemon is Ash's story. There would be absolutly NO point in changing characters. Why? I direct you to Richie in the Chronicles. Oh yeah, whole new character he was. He reacted in ways that you could never imagine Ash would! Like helping out random annoying people, annoyingly tolerable of helping out annoying people, defeating Team Rocket, kind, helpful, scratchy voice, Pikachu...oh yeah, completly different from Ash.
Even Gold wasn't that interesting. Seriously. Like, what was so different about him from Ash? Other than he was dubbed annoying phrases and had a Typlosion, I mean? They should've included Silver. He was in the Japanese opening.
If someone else becomes the main character I'm don't think I'm going to bother watching Pokemon anymore. The story won't be any different and every series is pretty much the same anyway. All we'd be doing is watching the same 500+ episodes just with a different character...