It appears Canon has solved the banding issue? 6D!

Horshack wrote:

There would likely be a big R&D hit to modify their firmware to support a different vendor's sensor. Although they've implemented Sony sensors on their P&S cameras (like S90/S95), to my knowledge they have never done so on a DSLR, and the firmware bases between the two are probably different.

If they're like most vertically-integrated chip+technology companies they probably stick to a common register interface and operational behavior between generations of chips, which makes porting the low-level aspects of the firmware easier for each new product. Introducing an entirely new chip design and interface would require a pretty significant change to the firmware, the extent of which depends on how well they abstracted the chip-level interface firmware logic from the rest of the firmware.