Update: very preliminary OTF font files are available here: scruss/AVHershey-OTF. These don’t yet even encode all of ASCII, so aren’t yet generally useful.
Major breakthrough: yesterday (Feb 5th), I got the old Hershey fonts outlined properly, and today I have compiled them (sorta) into vector fonts. They’re not yet ready for release, as they have no metadata and are missing some key characters (even for ASCII).
I based the line thicknesses for the fonts as if I were drawing a 16 pt character, and using a plotter with a 0.3 mm (light), 0.7 mm (medium) and 1.0 mm (heavy) pen. You can see in the individual characters from the Hershey Complex font shown below, that the double hairline strokes merge into thicker single strokes. The same effect occurs on a real plotter, too:
Here are some preliminary bitmap samples: