If you want to see similar technology that's being used now, check out the Leap Motion being used with the Oculus Rift. They mount it on the front. I've personally only got experience with the rift (I have a DK2), but I've heard good things.

I think Oculus has it right, though, in that any HMD that does positional tracking needs super low latency to feel natural. Should be a little less problematic since the whole world wouldn't lag, but I'd be disappointed if the virtual overlay had perceptible lag after using some of the better experiences on the rift.