[mst]

As far as I know, in the D850 will not be only lines to indicate APS-C usage but also a fully blacked-out area. So, I have one use for the additional Fn2 button: "Switch to APS-C. NOW!" 

The D3x can do this already  

Later cropping doesn't help me saving disk (or card)- space. But you're right, the D500 is less expensive and doesn't need a lot of furniture around the cam to be really fast. It has a touchscreen and tilt-display as well and uses the very same set of buttons and wheels.

 
...and batteries and memory cards