Comment by kortilla
It’s not “niche” if you do things synchronized to GPS timestamps. (i.e. a significant portion of telecom, a bunch of electrical grid stuff, etc).
Anything using GPS as lock references to synchronize stuff that needs to be aligned to the millisecond absolutely cannot tolerate stuff like “the leap second smear”.
"niche" doesn't mean "unimportant." It just means "uncommon." It's a relative term.
The vast vast majority of people using general purpose datetime libraries are not in need of GPS handling or high precision scientific calculations.