I wanted to document my comparison of the various options I have considered though :
|Kinect||58H (IR)/63H (RGB)||30||30||NA||£100|
The above table is incomplete obviously ~ I've thrown in the SII since I have one available but I can't find any specifications on the camera, even from the datasheet hence the numbers are a guestimate based on a comparison with the C910.
Doing the above research confirmed that I will have to rule out depth based systems such as Kinect and Asus's Xtion since the minimal operating distance for the IR camera is 0.5m in the case of the Kinect and 0.8m for the Xtion. I believe the kinects FOV can be improved to 90 deg via an add on lens but that obviously increases the expense. Pity but a conscious design decision that I am now making is to focus on the "natural gesture position" that I illustrated earlier based on the advantages of it being eyes-free. I am aiming to incorporate a forward aiming camera as well though so, yes, we're talking about a 2 camera system now (possibly with very simple homebrew IR modifications).
I think the main modification that is going to be needed is to increase the FOV of the camera and do so cheaply - some interesting ideas I uncovered for this:
Commercial camera wide angle lens
CCTV wide angle lens
Adapt a lens from a door peep hole
I like the idea of the door peep hole - a nice hack and within my budget.