I second Jan Anne's wish list. With all these buttons lying around, a reconfiguration to dual AF-ON should not be that difficult... including, possibly, firmware revisions for older cameras.
As the Df has become my main camera (instead of the D800), I wish it had a less cramped AF zone. The broad rectangular AF detection zone of the Olympus OM-Ds are just right, for instance.
Until now Nikon issued a "reduced size" camera, eg D3 > D700, D4 > Df built around the same sensor. I'd be curious to see what happens here. The D-one digit family is just not the right size for me.