Rear-facing seats are not illegal I think (obviously not allowed for the pilot, currently) - and they have been amply proved to actually be safer. They've been the standard on military planes (again, not for the pilot :-) ) for quite a few years.
Once people get around the initial shock (something not to be discounted - it may kill the sales of a car) they are quite happy with them on planes.
I think that's basically right. The worst crashes are usually frontal, and your entire body is evenly supported, rather than hanging on a seat belt or something.
Rear-facing seats are definitely not illegal in cars. Tesla has them as an option for a third row in the Model S. I think they would be legal in airplanes too, and the main reason they don't see more use is just that people are often uncomfortable not facing the direction they're going.
