Also, for those of us with serious winter, scraping ice and frost or even scrubbing bugs off a polycarbonate window would be a very scary process. They might offer Polycarbonate for vehicles going to warmer climates where they never expect to experience freezing conditions, but that was a concern for me. I don't know the relative weight of Transparent Aluminum (Yes Star Trek fans, it is real), but Transparent Aluminum would be a lifetime windshield which shouldn't chip, scratch or break where we get 2-3 years out of a glass windshield up here in the Colorado mountains with all the gravel on the roads in the winter. It would be 2 or 3 times the cost of glass up front, but should never need to replace. Option maybe???
Polycarbonate is fine for aircraft where sandblasting from road dust is not a concern.