Remember Jobst Brandt's solution to the pedal threading problem? He investigated using a conical seat in the crank and a tapered collar attached to or machined into the pedal shaft. Like this:
This is similar to modern cars' conical seat lug nuts/bolts, now used instead of the reverse-threaded-on-one-side flat shouldered lug nuts once used. He reported wrongward-threaded pedals staying put during the course of his tests.