I really agree with Steve Perry. IBIS is interesting, size isn't different enough to matter - lenses still need a bag of approximate the same size; maybe I can slip one additional lens in there. I couldn't care less for EVF, but any VF lag makes it a tool of the devil and having heard so many times how crappy EVFs are a thing of the past, check this one out - only to find the EVF is just as crappy and still a huge step back - color me intensely skeptical. One card slot is fine, since like Steve Perry I just pop a large card in my cameras. A grip is essential and I use one whenever practical. Battery life - no big deal, just bring a few more batteries. AF-S, never use it. AF-C - critical. I use it even when snapping informal head and shoulders as it only takes a fraction of an inch of head movement for focus to shift from iris to eyebrow, even when stopping down. The only way to deal with it is with AF-C continuously tracking head movement. Forget AF-S (too laggy, missed the moment), forget manual focus (misses the moment, other than the moment of critical focus, maybe).
On top of this, what does it do that a D850 doesn't? Err... uhmm... nothing, really. It just trivially changes the packaging. *shrug*
Okay, it does do a few things the D850 doesn't - perfect stealth silence for one. I don't personally care.
Now the red dot sight just announced... that looks potentially useful! But then sighting a telephoto is pretty easy by just keeping both eyes open...