Amazon is offering the Nikon FTZ adapter for FREE for the Z 6 (https://amzn.to/2TMqoCp) and Z 7 (https://amzn.to/2TLCuf4) when buying with the camera itself... So in case you thought of going mirrorless but didn't want because of your existing lenses - I guess it's an easier decision now.
Disclaimer - I don't work for Amazon or Nikon... Just a Nikon user contemplating on the matter myself :-)