This is great and all but how do they look? The only good example is the tape recorder which imho looks less and less like a real tape deck at larger sizes; the shape of the tape is noticeably distorted and the curves in the shape of the body are unrealistic.
Saving space is well and good but for icons it’s secondary to how clear and usable the images themselves are.
One of my favorite articles on this topic, "About those vector icons", goes into this issue and many more flaws in much more detail. There's nothing fundamentally wrong with vector icons, but it's not all that's needed for a one-size-fits-all solution.
showing some image using fewer and fewer pixels is like trying to summarize some text using fewer and fewer words, at some point it requires intelligence, at another point it's an artform
Haiku has an extensive UX and design guidelines document - including meticulous rules for icon design. The tape recorder looks that way because it adheres to those guidelines, not because of a file format.
Typically how they look is up to the designer, they can decide how many small details they want to put in to make the icon look better at a larger scale. Haiku seems to have gone with a kind 3d clipart style that isn't highly detailed.
When the format was developed nobody was rendering icon's at 128x128. PC Icons were 16x16 or 32x32. Mac's might have supported bigger icons, but it was still a long time long time before screen resolutions necessitated 64x64 icons.
Saving space is well and good but for icons it’s secondary to how clear and usable the images themselves are.