Yeah I posted on here about have rotating camera's in the hinge a while ago, as it would allow DSi backwards compatibility (one facing the user and one facing away from the user) and also allow 3D picture and video capture both towards and away from the user.
Eye tracking would be pretty awesome, however the system would have to know where the user is in relation to the screen being looked at to accurately track the eyes movements. It would also require a high resolution camera to be able to pick up the minute movements of the eye and reflect those movements into the game.
The other issue of course would be that the human eye doesn't move smoothly, it's very jittery movement and also I would assume that the camera would be controlled by the eye tracking, which would cause the same issues that the Wii pointer has in relation to bounding boxes. I don't think eye tracking on such a small screen would work, maybe Natal 2.0 could have something like that..
