At the very least, why keep Kamala Harris? Most Americans don't think she's qualified to be President. Every time they see signs of Biden's aging, they will be thinking of her stepping into the Presidency.
This is a good time to try to have a non-partisan (hopefully, cough) discussion. There's plenty of time to replace Kamala on the ticket. Do you think some Democratic voters would be upset that a minority woman is being replaced? The usual Democratic playbook would be to replace her with a woman preferably a minority. So perhaps it could be a wash from a demographic perspective.
Butler's point about "generic democrat" winning is misleading.
"Generic democrat" will always do better than "specific democrat" because it isn't a real person.
You can't use those numbers to make an argument like this.
To your actual point, other than FDR, has anyone
ever switched VPs in between terms and been re-elected?
I don't think the backlash would just be "replace her with an identity pick or we get mad", it would be a whole brouhaha about how it shows weakness, disloyalty, there would be infighting and sniping about whoever took the position.
I can't see it going smooth. Biden could probably pull it off if he was vastly more popular and in a position where he could sell it as a power move, but I just don't think that's the situation.