Someone with 5000 hours design experience needs to make a common icon theme for a few 100 GTK and QT libraries and standard-names. It feels like it's 1000s of hours of work. And then you have to make them available in a few formats, HDPI, maybe a build system, etc. there are a number of themes but the ones I try seem to be missing one or more of the icons from the set. Just need the right volunteers to build them, and also get a bunch of app-builders to adopt them, and figure out what colour the bike-shed should be (blue).