PS was actually used for OS graphics multiple times (with more adaptions of course)

https://en.m.wikipedia.org/wiki/Display_PostScript

Yes but using raw postscript in this perverse way to get interactivity is truly inspired. My hat is off to the author.

Not really, that is exactly how it was used in Sun NeWS.

https://en.m.wikipedia.org/wiki/NeWS

You would write full blown GUI apps in Postscript with some C glue.

Well, it really doesn’t. This uses a clever hack where you write the input to a text file that the PS program is continuously reading. Very cool.