Live fps, gps enabled

So I just read an engadget post about the tron bike game being replicated with cellphones and gps, but what about using technology to do this with other games. Like what about a lasertag like game where both people have gps and you can see eachother's location on a near eye display imagine how sweet that would be if you could get a city wide game going where people join one faction or another and the gun is just a highly directional ir laser. I personally would pay a ton of dough for a game like this imagine just walking through a city with a pair of sunglasses on that suddenly bring up a map informing you that someone is within killin distance. There are a ton of variations that could come out of this. Cause man would that would be a cool way to spend a saturday, walking through a dense urban area looking to pick off members of a rival faction.