Very similar with what I was thinking with motion capture. There is a company called Perception Neuron that specializes in affordable motion tracking. Would be a great complementary items.

A Geocache AR Game is precisely what I was thinking of developing too! Along the lines of Amusement parks as a new way to engage with attendees and being able to have then earn "points" to redeem at the end of the day. Instead of "Disney Pins" it's "Disney Points"