We are finally in the future where hidpi displays mostly make hinting unnecessary.

Even before now, hinting has been a highly questionable pursuit. I believe Freetype enabling its autohinter by default has led to ~20 years of most free software having tortured, ugly misshapen text.

I don’t think you can blame TrueType’s hinting for problems with FreeType’s autohinter, which was created specifically as a patent-free replacement for TrueType’s hinting (https://www.freetype.org/autohinting/hinter.html)

The autohinter was a noble attempt, and in some cases it eventually did a passable job. But enabling it by default is the part that I think might have been a mistake.

Yeah, that's what the developer mentions in the readme. I wonder though, is it such a big deal in the era of 4K displays?

We are quite a few years away from the 4K era.

4K desktop displays are still a blip in the radar (about 1%).

I didn't realize that the percentage is that small! However now that I think about it, mobile could be an excellent place to use this library.

Indeed, for mobile there is a good case!

Neither does OS X Quartz.

My understanding is that the macOS font renderer uses limited hinting for small pixel sizes. Of course retina displays mean most normal on-screen text is rendered at 16px or larger, so it's increasingly rare for hinting to matter.

Does this mean Mac OS doesn't have it at all?

No, just not quartz. Microsoft and OSX have some share in hinting