Optical position tracking of fingers was actually ok (but not on a bus, and not so much for stylus), and with a look-along-the-keyboard-surface mirror, even optical height and touch was ok. But the touch wasn't great, and occlusion was a "keep it always in mind" problem. So I would have been delighted to find say a low-precision multitouch textile, to hopefully drape over the keys without too-much impairing typing. To decouple a fast low-precision-XY high-precision-Z touch, from simple and adequate camera XY. But crafting a capacitive grid... seemed a yak too far. All this was yak shaving - I actually wanted to be exploring VR IDEs catalyzing improved programming languages. :/
[1] https://upload.wikimedia.org/wikipedia/commons/c/ca/ThinkPad...
Anyway, Apple has patents covering this idea. I believe 9,041,652 is the one I'm thinking of.
Commercial HID innovation seems to be bimodal, DIY and bigco, with a patent-induced desert in between. Take multitouch. Years of crippled small companies, selling kits to dodge patents, to small DIY communities (DIY historically being much less of a thing than now). Speech-to-text and Nuance. Hand pose from webcam and colored glove research, becomes of-course-unsuccessful startup, bought by bigco, and thereby unavailable to support further innovation. Leap Motion's DIY Project North Star is an ongoing example - there's software, and you can buy parts, but not devices. So while there's an active small-company ecosystem around say keyboards, that falls off really fast. Small-scale markets of oem support for exploration and innovation... aren't an interesting niche for bigcos. So they produce patents and not products, and even proven too-small-just-a-distraction-for-us markets are abandoned.
As education innovation starts overlapping ML and tech, it looks to be picking up similar dysfunction. Ah well.