I got the D850 a few weeks ago after waiting for it to become more readily available as an in stock item. Already own a D500 so I was not in major rush.There is not much I can add that others haven´t already said, but this camera is a sheer delight to own. Quality and sense of robustness are top tier not to mention available functionality and image quality. Owning a D500 I had zero learning curve with the D850 feeling immediately familiar in every respect, but with a few added features such as touch screen menu selection, focus stacking, auto picture control and so forth. I plan to keep both cameras using each according to their individual strengths. I mainly use the D850 for landscape and portrait. Many reflect concerns with the large file size, and I also shared this concern initially. 14-bit lossless compressed NEF files average around 50MB, just over twice the size of typical files from my D500. I do the majority of my post-processing using LR mobile on iPad Pro but still use LR classic on desktop computer especially to create camera/lens profiles and so forth. I was concerned that D850 files would bog the processing down on the iPad and desktop, but I was pleasantly surprised how well both LR mobile and classic handles the files. Sure processing is slower than with D500 files, no doubt about that, but still quite acceptable. It can take several seconds for images to reach full resolution, original format, but process is cleverly handled by lightroom making perceived processing speed acceptable in my opinion.
Must admit I was a little ´´perturbed´´ when the stellar Z7 reviews started to emerge, so quickly after I made a committment to the D850. To some extent this robbed me of my sense of delight with the D850, but I quickly got over that. I plan to keep the D850 for a good few years but will continue to monitor mirrorless developments. Perhaps when 2nd or 3rd iteration of Nikon mirrorless emerges I might be tempted over ;-)