It seems that this will be announced sometime next week, as the update for both the D800 and D800e.
From what I have read, it seems that it will have a bit better DR, in the higher iso range, somewhat faster frame rate, 1 fps, but I noticed that a "small raw" is being mentioned. This would be a nice feature as in some cases I am not in need of a full 36MP sized file, mainly in night work.
It seems it won't have wifi built in which was surprising to me as this seems to be pretty standard now on all modern bodies.
Current claim is that the body will be lighter also.
Build will be in Thailand, not Japan.
As far as I can tell announcement date is the 26th of June.