Actually it's currently in development and being used
I think what you are seeing there is a synthetic vision system Where the image has to track the users head movement and direction of gaze. So as to overlay a video image over the 'real world'. Tough to do, bulky and expensive.
The simpler HUD display being developed by Intel could display some of the interesting glass cockpit information without the need to overlay it on the outside scenery. But then how much use is repeating that info up into someone's field of view when it's already right there on the instrument panel already?