Just a few days ago, Nikon released the D810, a successor to the D800/D800E. The changes include tweaks to make full use of the high resolution, expanding ISO range (both ways) and adding a few video features. As usual, I advise you read the details on Nikon.com or dpreview.com
Externally, little has changed, which means that The Unleashed D200+ with the D800 modification will fit the D810 as well, and will work just the same as on the other Nikon DSLRs. The only change I know of concerning GPS functionality is that the top LCD (and likely the Info screen on the main LCD) now features an image of a Satellite instead of the typical [GPS] icon:
 D810 Top LCD new GPS icon |
 D800 Top LCD old GPS icon |
We’ve already seen this change on a few other new Nikon DSLRs, for example the D5300 and Df.