Here are some things I have gathered from the original orientation:
1 The gray colored part on the right appears to be a wire (the 6 wire interface to the NXT).
2 The holes on the left appear to be 3L apart, thus an overall hight of about 5L.
3 The top holes are about 11L apart, thus an overall length of about 12L.
4 There is a "gray plane" about 7 1/2L X 3 1/2L in size, relatively in the middle of the "item".
Here are some things I have gathered from the original orientation AND from orienting the image 90 degrees up in the front, so it appears thin with a bulge up on the right side, and a gray line representing the very end of the wire:
1 The "bulged" part (where the wire comes out) is about 1L thick, and the thinner part is about 1/2L thick.
Here are some conclusions that seem logical:
1 There is no forth hole, as it would be where there is likely the circuit (supported be the fact that the wire comes from there, and that there is a "bulge" to make room for it).
2 The "gray plane" is glass (or similar). Supported by the fact that if you look at the back, there seems to be a larger area that is sunk, making a nice "frame".
Perhaps an LCD? It does have an area near the "bulge" that appears to be a connector of sorts. I would however rule out an LCD based on the fact that most are not I2C compatible, and that the NXT already has one (not to mention that it is over twice as long as tall, not typical for an LCD).
Perhaps a touch sensitive area sensor to sense where you are touching? Possibly even using capacitive technology, as is in their new Number Pad (Which by the way, is AWESOME!!!). I am wondering though, Why such an irregular shape?
Another thing. What if the sensor "front" is actually the back? This would add a considerable amount to the borders, making the "gray plane" (glass?) about 8 1/3L X 4 1/4L.
Based on this theory, I would venture to say that THAT IS a decent enough size for a capacitance touch sensor. If it is, then you could make any front you wanted, by simply making an "overlay template" (go to the Number Pad product page, and there are some downloads that explain what I mean).
So far, my guess is that it is indeed a capacitance touch sensor.
Please post any known info or statistics that may help