A kinect will wait for two people to walk towards one another on the street, then it will make each one control a different fighter. Suddenly these people will be forced to interact and their body movements control the two fighters.
I also think something collaborative could be fun. Like street portal!
Random two people will be given a puzzle to solve together. One person can place portals by pointing to a location, the other is able to push the block around. And yeah, bonding with random people over portal. c: