The article misses the mark IMHO by focusing on skeuomorphic(sp?) icons.
Yes, usability has degraded during the recent 'flat design' craze, but not so much because skeuomorphism was tossed out, but because the many little visual design changes that kill discoverability.
The mobile operating systems started this trend where a lot of advanced functionality was hidden behind 'magic' touch and swipe gestures that go way beyond the simple and intuitive tap, zoom and rotate gestures, like 2-, 3- and 4-finger swipes, long and short touches, etc..., important features cannot be visually discovered (how do I close an application again, on iOS, Android and Windows8? how do I flip between applications? how do I take a screenshot?).
It's the many small things that kill usability for the sake of visual design:
- the famous shift-key on iOS, what the hell were they thinking?
- buttons are often indistinguishable from non-interactive label, leading to idiotic trial and error clicking to find out which UI elements do something
- scroll-bars that are hidden by default, loosing the information how far I am into a document (OSX)
- changing and moving things around just for the sake of confusing existing users, not making anything more intuitive (especially Windows is guilty of this)
And so on and on... the icon design is the least of the problems (and every OS worth its salt should allow to replace the icon theme anyway).
One important reason I'm going back to the command line more and more is because UIs have become so unusable for anything that goes beyond browsing an image collection. Change itself is only good if it results in improvements, but in the area of UI design, things that have been working just fine for 20 years have been broken for superficial visual effects.
It's like 90's web designers took over and are building operating system UIs now (and may be there's a bit of truth in it).
It's not like the past was perfect of course, I mean... Alt-F4, Alt-TAB, ... but that was on Windows which was always laughed at for its poor usability (at least from view of AmigaOS and MacOS users).