If they are using zinc chromate then I doubt we will see production cars with flat black paint. Chromium in the +6 oxidation state is pretty dangerous, and scaling its use up to an entire fleet of cars would have very high costs associated with it (safety and environmental). Costs that I doubt the consumer would pay for. Maybe special editions of exotic and near-exotic cars where conspicuous exclusivity commands high appeal to potential buyers. That’s the real reason people buy those cars anyway-to feel exclusive or different.