Nikon seemed to have settled with their 600mm at the top of their line-up. But NikonRumors now reports there could be an 800mm on the way...
While there were supposedly rumors of an 800mm f/4, this one will likely have ended up an AF-S VR 800mm f/5.6. Still, this fills a gap Nikon has had recently, considering their last 800mm was originally released in 1986.