Nikon Rumors picked up word that a new AF-S 800mm f/5.6 VR Lens should arrive in September around the time of Photokina 2012.  The longest current lens in Nikon's line up is the 600mm f/4G ED VR AF lens.  Given that this lens is priced at $9800, I would expect to see the 800mm lens in the same $14k ballpark as Canon's 800mm f/5.6L.