Can Google use proximity sensors to show/hide soft navigation buttons in Nexus phones?

I've had this idea since I started using my Galaxy Nexus, but I thought it needed some hardware from the future which senses the heat from the hands when the fingers get close to the glass! (stupid I know). Anyway, I just went on a quick search about proximity sensors and they work (place the phone near your head during a call and the screen auto-shuts off), and it seems that is all of what is needed to implement idea the way imagine it.

Imagine proximity sensors in the area where the LED notification light is in the Galaxy Nexus (and Nexus 4), the lower bezel area. When you move your finger near the lower part of the screen, the navigation bar glides up quickly. Move away your fingers just a bit, it glides back down. Otherwise, it's always a full screen.

Do you think such solution is viable? If yes, do you think it can be convenient?

Thank you