Clever, but, I would imagine the camera has to be stationary relative to the measurement plane. And then you need a stationary car which means a wind tunnel, I suppose it could still be useful leaning out a window or sunroof. At that point it makes sense to just do CFD.
edit: but with some development of the tracking camera that could work out sizes, then maybe a stationary camera wouldn't be necessary.
Julian, this may be of interest