Seems like there's a lot more entertainment potential than military.
Not trying to start a flame war, but I believe that modern video games are prepping for that. If you've played any of the modern shooters, you need to be good at keeping an eye on your HUD while tracking targets and navigating through your environment.
you could probably do some sort of reverse retina scan to make sure they're only used by the intended wearer
the threat of hackers applies to any number of technologies currently in use by the military
human causulities are the biggest limitation on the projection of US power, you might as well work on the assumption that you have to emerge from every battle as unscathed as possible