According to this patent diagram* shown above, Nikon could be readying an autofocus 800mm f/5.6, presumably to be called the AF-S Nikkor 800mm f/5.6G ED VR. It comprises of no less than 16 elements in 14 groups, the last element (on the extreme right) being a drop in filter and part of the optical construction. This design doesn't show a meniscus front filter, but that could be added easily enough.
The construction shows internal focusing (IF) at G2 and VR compensating optics at G3, the latter accounting for the high number of elements in telephotos these days. It's also safe to assume that this lens will also feature a SWM and Nano Crystal coat. If we're to guess, the lens was designed with the intention of being produced in time for the 2012 Olympics, though after the events of March there might only be a handful ready by then.
The Olympics would be too good an opportunity to miss using this with the new mirrorless V1. Used together ( it would also need the announced FT1 F-mount adaptor) with the camera's 2.7x crop factor the lens would be the equivalent to a 2160mm (in AoV), and would be able to shoot at 10fps complete with AF (central AF area only). Just imagine the possibilities (and where you read it first). For stationary subjects the V1 will shoot at 60fps (it loses AF) but will only capture 30 frames (that's just half a second of shooting) before the buffer is full. Oh well.
Nikon's last 800mm f/5.6 was a manual focus AI-S lens, with 8 elements in 6 groups. The Nikkor 800mm f/5.6 IFED, shown below weighed 5450g and was produced in batches between 1986 and as late as 2005, though I can't actually believe that they made any after 2000. The AI-S 200mm f/2 IFED was shown in brochures and on Nikon websites for years after it had been removed from production.
Rival Canon pioneered the 800mm f/5.6 producing an L-series FD breachlock lens for the F1 system back in the late 70's. That particular lens was designed for tripod use only, as was the later Nikon version. However the new EF 800mm f/5.6 L for the EOS 1 series was designed to be handheld, and is around the same size and weight of the current EF 600mm f/4L (though the new version is slightly lighter and smaller still).
Nikon's first and only manual focus AIS 800mm f/5.6 IFED model (above).
Optical construction of the rival EF 800mm f/5.6L, neatly showing the IS optics and focusing group.