I kinda like this idea for UX customization, because:
Qt already supports it -- it's basically just a global limited-function CSS stylesheet
it's well-documented already by the Qt folks
pretty much all I have to do is give each of the UX components a name, document them, load the stylesheet at startup (or when the stylesheet changes), and that should be nearly full customization for anybody who wants to, without reinventing a whole UX to do it. Because it's auto-refreshed on change, that's a simple way for people to experiment and see their changes applied immediately. Oh, and I should probably switch everything over to using just the stylesheet for colors (no hard-coded colors), and I should stick the default stylesheet in an obvious place (perhaps Contents/Resources?).
https://doc.qt.io/qt-6/stylesheet-reference.html