@herzenschein great intro to #KConfig, #KSharedConfig.
This issue has bugged me ever since and many years ago, back then when #XDG was introduced I tried to steer several times into a direction as what you outlined in your post but unfortunately the idea never gained enough traction to do it "right" from the very start.
Nowadays, I'd love to see other backends for KConfig - e.g. I'd like to be able to use @charmcli's Skate [1] to sync my #KDE configs across devices.