Another +1 … while my 4C will be used with a Windows machine for gaming, for development and operations I live in a multiple-monitor Linux world, and something as simple as a mouse pointer moving to the gaze position on demand (double-blink? 🙂 ) would be outstandingly good.
Whether this is integrated as a HID + control panel or simply presented as an event stream that needs a specialist receiver program isn’t too important, it’s easy to remap co-ordinates and introduce new inputs events to X, even just using xdotool(1).
Of course, there’s a presumption that the device is doing the processing onboard; if instead it’s offloading much of this to the drivers then the fuller SDK may be needed …