Sooner or later the backwards compatibility of the "F" mount has to yield. However, it is pretty surprising, and dare I add, heartening as well, that you can mount lenses from the late '50s on a modern camera like the Df and the combination just works.
Many users frown upon putting old lenses onto a new camera, as they focus on the features that are missing and believing such are critically important to get a picture at all. Each to their own and many Df users know better by now. If you can make it sing for your own photography, go ahead and that is where Nikon stands out by allowing for so long time. Of course issues begin to develop in the compatibility matrix over time, anything else would have been a sensation. But again, that is not the point.
Seen in the above context, 'E' lenses break compatibility in one direction: few if any old cameras can use them. However, most of the new cameras can, and it is pretty certain all new Nikons to come will support 'E'. Thus the traditional ever-lasting Nikkors just potter on, as long as their support is provided by the camera. Nikon Df shows this all-encompassing support is possible even in the most modern of cameras. Let us hope that tradition continues into the future.