Good luck with that. The problem is that no one will make a UI/UX that's both awesome and stable. It's not like the resources aren't there: there's a ton of DEs for Linux, and they've been working on them for 20 years now. But the problem is they can't ever agree on anything, and they can't ever just leave well enough alone: every time they get something stable, they abandon it and make up something completely new and unstable. It's easily the 2nd biggest hindrance to Linux-on-the-desktop adoption (the biggest of course being application compatibility/inertia with Windows).
>but that's where the fun stops. Linux UIs tend to lag behind significantly.
That's the Linux community's fault. It's not the features that lag, either; KDE, feature-wise, has always been far ahead of the commercial UIs. For one simple example, I can't middle-click and vertically maximize a window on any other DE that I know of, but in KDE that's been a standard feature for at least 15 years. For another simple example, multiple desktops have been standard on Unix UIs for over 30 years, but never in Windows or Mac. The problem with Linux UIs isn't design, it's stability: everyone's constantly revamping stuff (Gnome3, KDE4, KDE5, etc.) and never spending any time fixing bugs. For instance, I have the Dvorak keyboard set on my LM17.3/KDE desktop, but several KDE apps don't respect that and go back to Qwerty. (To be fair, Windows is even worse: I have my work Win7 desktop set so I can switch between Qwerty and Dvorak, and the stupid thing is constantly switching back and forth randomly.)