There’s a proposal at the linked blog post for how to clean up the config directory.
The post goes into detail which changes would be required in KDE software using Qt.
After reading, I just have one question (the blog does not seem to have a comment section): how does this handle transitioning from the old location to the new location? Imagine having a katerc config file under ~/.config and one under ~/.config/kate (which is the suggestion from the post) - should those be merged once and then the old one gets deleted?
I answered something similar elsewhere:
Just for clarification: this would be a one-time process per application, right? I’m sure this will work for 99% of users, but there’ll always be the one (or a couple of users) that synchronizes their .config directory, then doesn’t update all machines at the same time and all hell breaks loose - a.k.a https://xkcd.com/1172/ :-) But I’d say that’s probably not worth losing the advantages of a cleaner .config-directory, so this might be one of those “tough-luck” situations… 🤷