Fun read. However, if the suggestion is that we force ourselves to constantly update iconography because the metaphors are outdated, I don't agree. Sailors still say "knots", but I bet young ones don't all know why. People say "breadboard" all of the time when building electronics.
Similarly, the very letters of our language evolved out of symbols that meant something to some humans long ago, just as words have an etymology.
People simply start to associate icon with action. Mail on my Mac is represented by a postage stamp. I never realized that until I just analyzed it. Good icons are subconscious like that.