Honestly, I believe the only benefit the D4S owners will see is an improved video functionality to bring it on par with the D1X, an improved AF performance, which Canon already addressed with the 1D x firmware version 2.03, and higher FPS, for whatever it's worth, once again to bring it up to speed to the 1D X, all for a price comparable to the 1D X. Basically closing the gap to the 1D X 2 years after Canon released their flagship.