I have got to use HUD in my car for a few weeks now and have been wondering what does it take for our great EIFS providers to add this to their system. It has been really nice using it in the car and would imagine how nice it would be to have it in our cockpit.
The new Garmin device is just a display unit. It works with your iPad / iPhone running Garmin apps - so far only the road (non-aviation) apps. But I imagine it wouldn't be hard to adapt the aviation apps to work with it as well.
Garmin has been pretty good about carrying the early G3X adopters along as they systematically introduce the next gen G3X components. Blue Tooth seems to be an integral part of their newer offerings. OshKosh should be interesting this year.