Spread this information to any sushi chefs you know. The opportunity to help sustainable fisheries by eating puple urchins into obscurity is huge. It's what our economic system is best at.
By "inedible" I didn't mean that purple urchins taste bad necessarily (acquired taste). It's just that shelling them takes so much work that it's not worth the effort for chefs. There are millions and millions all along the coast; convincing a few people to eat them won't make a dent in the population.
Even if there were an increase in demand for the purples you'd still be hard pressed to get them commercially, California has been squeezing the number of licensed commercial boats down to about 100 and the market's flexibility is constrained by that.