According to recently report from Sankeibiz from Japan, Nikon is currently developing their upcoming Nikon full frame mirrorless camera in rapid pace, and will be released before March, 2019 (Nikon’s fiscal year will end in March 2019). And the announcement of Nikon full frame mirrorless camera could be around Photokina 2018 in September.
Translated from Sankeibiz:
And of course Nikon, who is very strong with dSLRs, is also advancing development of a mirrorless camera at a rapid pace. Nikon intends to begin sales (of their new mirrorless camera) at some point during the current (fiscal) year, it has been revealed. There are also whispers, according to someone connected to the industry, that “surely Nikon will unveil their camera to the public at a major overseas trade show.”