I have been holding off this post for few weeks now, hoping to get some additional information. Well, I did not and since it has been very slow on rumors, I decided to post this anyway. As of today, take it with a grain of salt:
I received a tip that Nikon is working on a new D810s camera that should be announced soon (in the next few months). I do not have any details or specifications, but I am guessing that compared to the D810, the new D810s will have a better high ISO performance and maybe few other improvements. It seems that Nikon is not yet ready for a big jump to a D850/D900 camera which explains the different D8xx variations (D800/D800E/D810/D810A/D800S). They also know how to “squeeze” better ISO performance out of existing sensors, so a D810s makes sense given the current “wait and see” approach.
