Focusing too much on style can be a bit of a problem, though. All too often, Linux theming and UX feels very "skin deep" - and obviously, It'd be great if most people focused on stability and robustness at this point.
First HN comment: "I wonder if we could use AI to replace the large-scale creative work of making sets icons."
I tried using MidJourney to generate exaggerated UI themes (not skins, just general themes for inspiration), but the results were disappointing. They were always gorgeous[1], but my prompt engineering skills couldn't coax it to use space efficiently.
the open source modular synthesis software VCV Rack has a UI composed entirely of SVG descriptions (even though 95% of the UI is provided by 3rd party modules that get loaded into the main program). They can look like anything you want, but the result is an infinitely (more or less) zoomable/scalable UI.
(That was before the Steam version ofc.)
Note that parent meant the UI holistically, and not just icon sets.
AFAIK, this way of thinking about the design of the entire system, and not just in discrete segments is largely unique to macOS. I think it is because Apple has a design language they try to enforce as rigorously as possible, even onto 3rd party developers, which gives the OS & all applications on it a very uniform and consistent feeling.
Windows is the worst. Microsoft has a design language, but they barely encourage it even among their own apps (Settings vs. Control Panel as one example).
I will make a strong claim: I don't think any O.S. developer takes design truly seriously besides Apple. Definitely not Microsoft, partially Google with Android, and certainly not most *nix distros (with the possible rare exception like System76's Pop!_OS).
I personally really like the Adwaita icon sets much more than windows and at least on-par with MacOS, though MacOS has the advantage of being rendered only on extremely high DPI screens. So most people only have that experienfe
At most would take me a week or so to do I think, more likely less than a day.