Talking to other attendees of EMW, I voiced my scepticism of the need for this over CCTV image analysis. My instinct was that a reasonable CCTV setup would get you 80% of the way towards your goal. I bumped into someone with professional experience at image & video analysis - turns out that the limitations of video are such that this sort of remote monitoring would actually give better quality data than camera feed analysis, at least if you factor in the relative cost of installing adequate enough cameras.
The biggest use for a system like this probably isn't gaming, home automation, or remote monitoring. Imagine instead knowing not where people are in a shop, but roughly what they are looking at, how they are each moving, tracking it all the way through to what they buy. Whilst there are lots of exciting security uses for systems like this, shopping analytics is where there are clear financial gains to be made (remember that investments to reduce costs typically look for >20% savings, but when increasing revenue 2% can be a lot!)
Of course, the big question here is range, and how many simultaneous targets this can track.
(and as a final note: now shrink this and give me my motion sensor alá Aliens ;) )