Here is my personal opinion for me relative to this comment. I really don't like the idea of being forced to carry two camera bodies. Also, living in the 14 FPS realm for a couple years ... the other day I forgot to change cards and was at 12 and wondered, what is wrong! People say, just anticipate the moment but human reaction times just don't align with that being a great solution and, while there is a sane limit to what is needed for FPS, I would not be happy with less than 14. Here is a mundane shots that kind of illustrates how 14 FPS helps in capturing a moment.I wonder if the next "pro" camera will be more along the lines of a souped up mirrorless 5Div. Something more along the lines of a Nikon 850 at about the same pixel count, slightly more or slightly less, and 8-9 fps and dual or even quad pixel. This would give the 8000 plus horizontal pixels for high quality 4-binned pixel 4K video.
This would be the ideal sidekick camera to a 1DXiii able to work with the same lenses and provide fallback in case of a failure, plus give access to some superb RX lenses at the shorter focal lengths. Also, this would be more the general pro camera for nearly everything not needing bombproof construction and 12-16 fps. If I were working high end sports, NFL, NBA, NHL, Olympics I would be very happy with this combo, 1DXiii and 400/2.8 and converters, super R with RF 70-200/2.8, RF 24-70/2.8 and perhaps a 15-35/2.8 for just in case. I kinda like that combo for wildlife and general nature work, too.