Nikon firmware has been decrypted by Simeon Pilgrim (with the help of Vitaliy Kiselev – the person who hacked the Panasonic GH2 firmware). The decryption worked on D5100 and D7000 and is currently being tested on higher end models.
The decryption itself doesn’t mean much at that point, but it may offer some neat “adjustments” in the future.