Dpreview has their review up, and it's funny looking thru the posts on the fm Nikon board. AF issues, need more shutter to not show shake, etc...
I can tell you, after owning and shooting 2 5DSRs for 1 full wedding season, that this will be the #1 issue by far with the D850.
The counter argument from the same 5 people, over and over, is that it is impossible for a higher megapixel camera not to out resolve the lower mega-pixel camera.
The reality of the human brain is that the higher megapixels creates a sharper more defined area of tack sharp focus and then the graduation begins away from this area - and then the human brain picks this up and sees all the areas that are not 'in-focus'.
When you combine the above, with scrolling through your latest 100 pictures you just took in your LR catalog, you are then further pissed that only a few are really, really sharp (i.e. why you bought the new fancy camera) - and you then ask what is wrong? Then you start running experiments to see what it takes to absolutely nail it focus wise - and then you lose your mind about all your non IS lens, your inability to really calm your hands, did you drink too much coffee, etc, etc, etc.
Nikon is going to cost all new D850 owners a lot of money because while they just bought a nice new $4,000 camera (with grip and battery), they are going to almost certainly now want the very expensive Nikon 24-70 F2.8 VR - and then they are going to want a non existent 85 1.4 VR, a 105 F1.4 VR, etc, etc. - alternatively, I think for near certainty, Nikon is going to singlehandedly sell more Tamron 24-70 F2.8 VCs than Tamron could ever imagine selling on their own.
I can't believe I'm even saying this, but I'm considering selling a 5DSR and an A7Rii and picking up a D850 with a few Tamron stabilized lenses