There had been discussions of noise performance comparisons between the Nikon D800 and D7000. Note that the D800 has a crop mode that shoots at approximately 16Mp (down from 36Mp full frame) when a DX lens is attached.
Now assuming that Nikon has not thought of this yet:
That remaining dark 20Mp can be used to perform on-the-fly dark frame subtraction. Normally this process requires two shots with the second shot performed with the shutter curtain closed or with a lens cap. If the original shot took 1 minute, the dark frame will also take another 1 minute. Waste of time. With this idea, there is no need for a second shot.
This idea can be expanded to other sensors as long as the sensor is slightly larger than the lens image circle. That means not only Nikon can do this trick but other cameras as well. Sensors are getting cheaper but the availability of quality crop lenses abound. This means crop sensor cameras can utilize existing lenses in a slightly larger sensor to improve noise performance at long exposures and higher ISOs.
I hope I’m the first to have thought of this.