According to dpreview forum user, he just some confirmation from NPS user that Nikon will soon announce a new AF-S NIKKOR 600mm f/5.6E PF ED VR lens. This lens will also be a compact lens similar as 500mm f/5.6E PF ED VR lens (Amazon, B&H Photo Video, Adorama).
Here is an updated rumored specs list of upcoming Nikon cameras and lenses to be announced in 2018. In the next several months of 2018, Nikon is expected to announced around three new cameras and 2 new lenses. At least one of these cameras will be long awaited Nikon full frame mirrorless cameras, and Nikon D760, D5S is also rumored to be announced next. Below are a list of rumored Nikon cameras and lenses to be announced in 2018.