I can't find it but I thought I saw an interview with a Nikon manager somewhere stating that their focus is on mirrorless, at least for the time being.
Personally, I don't think it will be feasible for Nikon to keep up both F-mount/dSLR lines and the Z-system much longer moving forward, and it wouldn't surprise me if the D6 and D780 are their last dSLRs. Not sure about new F-mount lenses either, although Nikon Rumors has reported about at least a new 200mm f2 to replace the now-discontinued VRII version. I'm not rooting against their f-mount OVF line by any means, but I'm not sure the camera market on the whole is big enough these days to support both camera lines. Time will tell I suppose.
I've more or less come to the conclusion that I'm all mirrorless from here on out re: FF35mm. I still like using my wife's D800 from time to time, but 9.9 times out of 10 I end up picking up the Z6.
Nikon needs to do things that set them apart from other camera companies, things that strengthen their reputation as a company with "long lines". They are not Leica (who is apparently fine with three lens mounts, one of which doesn't even support AF), but they certainly aren't Sony. If they decide to only produce the latest technology, possibly the most profitable one, customers may as well buy Sony or Panasonic.
There are many examples of "classic technology" doing well long after a more modern, presumably superior technology has been presented. The Leica M has been mentioned, Technics turntables that were discontinued but are now sold in 7 different models (while the CD is dying or dead), rear-engined sports cars etc.
Transitions like the one from DSLR to mirrorless is mostly driven by marketing and profits, and only to little degree by customers' needs. When I found out that I couldn't any longer go to a local shop to buy a DVD to watch in the evening, and certainly not a DVD player, it annoyed me endlessly. I have no need to pay a multinational company a monthly fee to choose between a zillion movies that they have picked for me. Streaming technology is mostly good for Netflix and Spotify. Marketing tells us that it's good for us too.
Yes, I use mirrorless too, but I want to have a choice, and I want the choice between the latest DSLR and the latest mirrorless technology, I want them to be similar and compatible, like the Z6 and the D780. If it isn't, I'll choose a Panasonic mirrorless and a Pentax DSLR. I hope Nikon knows that. I think they do.