Personally, I will probably never go the mirrorless route. My reasons are is that I still like looking through a viewfinder and being able to frame the shot just like I want. I never have liked electronic viewfinders and probably never will. I may be biased there but most pro photographers feel the same way I believe. Not that I am a pro, but I have been a photographic enthusiast for many, many years.
Yes, I know a lot of elderly people who have not learned to use a computer. I guess the same folks will be unable to adjust to the mirrorless, but that age group is likely to be gone before long, and the younger people buying cameras will not be asking for 850's. The fact that you Fellas have been using the mirror and prism for "many many years" means you won't be using it for too many more. And the new crop of professionals and enthusiast amateurs will be buying the mirrorless Professional cameras made by Nikon and Canon.