My D800 I rate as one of the most accomplished all round cameras of recent years. I D810 was a minor update and I did not think it was worth upgrading.
At the recent Lincoln Photography Show, I got the chance to use the new Nikon D850, at it is a very different beast. Its the best bits of the D800, together with the professional D5 and a new 45.7 MP sensor.
A number of magazines and photographic organisations are now starting to vote for camera of the year for 2017. The top candidates are likely to be Sony, Olympus and Nikon. I think Nikon will will, the D850 is hard to beat, high resolution rivalling medium format, as fast and responsive as the professional Nikon D5 but in a smaller and lighter body.