I put together simple positional tracking using a Kinect v2*.
The new Kinect uses a time of flight method for the depth sensing. For this it emits a pretty strong IR light that produces a nice IR image. I stuck a small piece of reflective fabric to the front cover of the Rift and used the depth map to retrieve the location of the reflective marker.
The results are probably nowhere near those of the Crystal Cove prototype, but it's good enough to experiment with and couldn't be simpler. The new Kinect has a very wide field of view and a (preliminary) range of over 4 meter. Of course with the single marker setup, it loses tracking if you rotate your head more than 90° away from the Kinect.
Using the Kinect body tracking seems obvious, but I think this method has less latency, higher accuracy and the Kinect only needs to have line-of-sight to the marker.
*Kinect for Windows v2 Dev Preview: This is based on preliminary software
and/or hardware, subject to change.