Conclusion: The D810 is still a superb camera which for most photographers will be the better choice.
Well the d810 is due an update soon, with the D5's AF system (or some adoptation of it). There is no point in not making the high res model have the best AF; the linear only points outside of the center columns is (and always was) very limiting and an absurd design decision IMO, basically most if not all portrait orientation full body shots suffer from not having reliable AF on the face, this affects portrait shooting, concerts, sports etc. I think the broad coverage with cross type AF sensor points in the 1D X / 5D III allowed Canon to obtain a stronghold even with lesser image quality sensors that they had at the time compared to Nikon. In a high resolution camera, reliable AF is paramount to actually make something out of the increased resolution (unless it is used for landscape etc. of course)
I would expect an announcement of the D810's successor later this year.