The big unknown, as best I can tell, is whether it's constrained supply or overwhelming demand. Either way, they're hard to find.
Last fall, I looked carefully at both the D850 and A7RIII and decided that after a few years with Fuji, the joys of an EVF, and the lack of a need to calibrate autofocus, that mirrorless was the future. I got on the list at my local store and got the A7RIII on release day. I suspect I'd have been happy with a D850; it appears that those fortunate enough to have received one are quite pleased.