Cool, I had the same basic idea at one point to do this with an Arduino. I wanted to have infrared emitters below the keys, and have an infrared sensor somewhere slightly in front of the keyboard (but at finger height). Your fingers should reflect infrared light back to the sensor. Not sure how accurate it would be, but I think it would be accurate enough to capture sweeping gestures such as your hand moving up/down for scrolling. Something like this wouldn't be precise enough to replace a mouse, but definitely useful enough to improve workflow (scrolling, switching between workspaces, apps, shortcuts). If the keys were clear, I'd imagine it would be even easier for the sensor to determine where your hand is based on how much infrared light your hand is reflecting back from different positions.
Very intuitive stuff, I hope to see this in laptops soon.
Very intuitive stuff, I hope to see this in laptops soon.