As to why they don't make guitar and harp strings out of the stuff, I don't
know. Perhaps it is too strong; the %T would be too low.(?) The floss is
available, perhaps some of our string-making friends would like to
experiment!
Thomastic does make a high-density nylon guitar string, their "C" series. At
a given pitch/tension thet tend to be about 25% smaller diameter that the
normal nylon strings, and they have a brighter sound. The "C" series strings
also come right up to pitch and don't stretch nearly as much as the normal
type of nylon. Perhaps we could get them to make some up for harps?
Finally, as long as I'm on the subject, most steel strings are plated with
tin to keep them bright. Thomastik uses brass to plate their steel strings,
and they do feel nicer.