That technology already exists. Just nobody wants to use it in an automobile.

awesome man someone's gonna make a killing when they do this. I'll buy it.

Would be good for security so people can't see inside your car when it is parked.

There is already such a feature in use for VERY high-end car roofs to have an open-air effect, but LCD is just strictly a display, but it only blocks 20% of light (80% transmittable) and is very susceptible to heat (if the car is hot enough, it will become permanent), whereas the lightest shade of tint is about 50% as far as I know.

As for that technology, it is VERY expensive to obtain, since that car that I mentioned runs for about $100,000 + USD, so I'm guessing it'll take a few thousand dollars to install, whereas I got an excellent tint job for my car for about $125 and still be able to see at night, despite the fact that I have "limo tint" or 20% transmittable light.