With HiDPI/Retina displays, that 24px is actually 48px or 72px, so the need for pixel hinting is much less commonplace than it was 10 or 15 years ago.

Also, nothing's really stopping most developers from just scaling it naively to those tiny sizes, in fact it's what commonly happens.

I agree we should keep support for custom icons for each size, and it's probably a best practice, but shouldn't be a _requirement_ anymore.