Let`s freeze the sensors

If you look at some of the big astronomy telescopes you will see systems in place doing what you propose - having the sensor cooled to low temperatures to improve noise performance and get the best quality possible.

The problem comes from the scale - it is technically fairly simple to cool down a sensor in a big stationary system such as a telescope where you can add on as many pieces as you like. On the other hand in a small hand held camera it becomes something more of an issue - the space required to build a cooling system in, suitable ways to vent heat, the power demands of the system and the fact that in a small camera not all the pieces like being cooled - drop the temperature of the sensor and it may very well work better, but drop the battery by the same amount and you will find a massive drop in performance (which is why battery life becomes an issue when shooting in low temperature conditions)

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