Add four autofocus sensors with the D4's center sensor's specs. Place those sensors at the 1/3 rule placement points. The D2X had sensors toward the edge of the frame and I miss that in Nikon's FX cameras.
Integrate GPS. I use GPS but it is a pain using external. Allow users to shut it off to save energy. Allow hard coding of one location as a default location when nothing else is found (like a studio or stadium location.)