I bought an Olympus OM-D E-M10 with an Electronic Viewfinder. I was really concerned about jitter, lag, graininess, etc, but it is excellent in all respects. It sure makes the camera compact by getting rid of the pentaprism you find in true DSLRs.
Now obviously not in the same league as this helmet, but the technology does get better. I can see where lag and jumpiness of image would really nauseate pilots.
Of course, with the camera, I don’t have an external reference so I wouldn’t notice the lag. With the helmet you are overlaying the image on the real scene you see before you, so it has to be instantaneous. That has to be very hard to do.
What is an Electronic Viewfinder?