IDK why people are interpreting your question about the mechanics of everyone switching at the same time. It sounds to me like you’re asking more about the bigger picture problems it would solve with society, not whether the sudden change would be able to be handled by the banks. Is that what you’re looking for?
Moving to a credit union is a great idea. I did a long time ago and haven’t looked back.
There are some things they don’t offer, sure, but then for stuff like investments I use dedicated platforms for those which is a better experience anyway.