It will be interesting to see where Nikon take the upgrade of the D5. Adding features in the D850 is likely, such as the silent-shutter, focus peaking, focus-stacking and improved touchscreen capability.
a side subject somewhat off topic - the D500 confers 10 fps out the box. The wider AF coverage in the viewfinder is a big plus too, even though the D850 can be shot in DX mode. Cost is the major deciding factor for many photographers. So for some of us, the D500 is a cost-effective backup to the D850, especially for action: wildlife and sport etc.