In an interview with the Japanese TV network NHK Nikon confirmed that their new High End Mirrorless System camera(s) will hit the market in Spring 2019.
There is yet no reliable rumor about the possible specs. But our best guess is this:
1) Nikon will announce an entry level FF mirrorless first
2) It will obviously have a new mount and be fully AF compatible with existing F-mount lenses with the new Nikon adapter
3) It will have a new 30+ Megapixel sensor with PDAF