The Windows 7 UI has aged pretty well too, even if the glossy visuals have become somewhat outdated (though personally I think they look better than modern flat stuff). I rigged up an old laptop of mine with 7 not too long ago and plugged into a modern monitor and it was striking how nice it was compared to 11.
High-fidelity 1-click reproductions of XP/7 for Linux would be very popular, I think. Bonus points if they can use the hundreds (thousands?) of XP and 7 msstyle themes on sites like DeviantArt.