I think that could be improved with a higher resolution sensor, but the question is whether you could build such a thing while retaining space for physical keys.
IIRC, current gesture recognition still takes a couple hundred milliseconds on modern consumer touch screens (iPhones, etc.), especially for the "click" action.
A lot of plastic is already IR transparent but totally opaque in the visible spectrum. You can hack a cheap camera and take out the IR filter to make a neat "xray camera".
Maybe you should do that and write a paper about it. :)
My initial thoughts: 1) is there space underneath the key for such a sensor? 2) would the infrared light bounce off of the plastic on the key? 3) would transparent keys affect chicken-peckers (and other users) adversely?
Not saying it's not possible, although I imagine there will be challenges.
IIRC, current gesture recognition still takes a couple hundred milliseconds on modern consumer touch screens (iPhones, etc.), especially for the "click" action.