Just realised that book Icons are another one that will probably lose meaning over time. That'll apply to book icons for dictionaries and thesauruses too.
Phone icons are already pretty odd as many kids would never have seen a phone that looks like those icons.
And the Save icons that are a picture of a 3 1/2 inch floppy disk are basically meaningless now.
I had to laugh when I heard a kid who saw a 3 1/2 inch floppy for the first time comment that someone had made "a actual save icon". I suppose that's how it seemed to him.
The open icons are often manilla folders. They still have some life left in them but not much.
There are still some clipboards around but not many.
Video icons that show sprocket holes each side of a film are basically meaningless now.
All the mail, email, mail merge, etc. icons that show letters are fast becoming meaningless. (Ask Australia Post about that) And adhesive labels?
Even the latest versions of Office (2016) have old style lightbulbs for ideas. That'll quickly be meaningless.
The slideshow icon in PowerPoint is an old style roll-up projector screen. And it's timing icons are all analog clocks (limited lifespan). It's screenshot icons are cameras that very few kids would recognize.
And so on and so on. I wonder how long it will be before many of the icons that were designed to represent common physical things will lose all their physical equivalence. Does that then make it harder for newcomers to computing to recognize anything?