UPDATE 8/23/12 - Apparently, this is a service modification only - please discuss the option with your local Nikon service centre.
Nikon UK has just confirmed to the DJP that the 36MP Nikon D800* has interchangeable focusing screens. While some controversy surrounds Canon's decision not to include interchangeable focusing screens on the new Canon EOS 5D Mk III, the option, either for OEM or replacement screens, is considered essential for precise focusing with MF lenses such as those from Carl Zeiss. Nikon users with older manual focus AIS lenses will also be able to benefit. If only Nikon would just re-introduce the folding AI meter coupling lever from the 35mm F3/F4 models then the majority of Nikon lenses dating back to 1959 could be used.
(*and presumably the D800E, though that's not confirmed at this time).