This is exactly what I was looking for. I've been thinking about trying to do this and thought arduino would be the only thing possible to pull it off. Sure enough, after 2 google searches, I found this. The only way (logical, safe, size appropriate, etc.) I see this being possible is to have a lens on the outside of the helmet. GoPro makes ridiculously strong mounting units. I'm going to try to take an LED screen, reflect it of a small mirror and on to the clear peice of plexiglass that you would see... I'll be trying some things out and will post any findings. I'm a little new to the arduino world so expect it to take a while... I think I might be able to solve the "focus on infinity" problem by obstructing the image on the LCD screen... We'll see i guess. Lol
How about trying a transparent LCD? Its super easy and simple, if you choose to have white it will look super transparent then you can add graphics so its as if its not there...