Seems like someone has something in the works: https://www.diyphotography.net/this-super-slim-adapter-will-let-you-mount-sony-e-lenses-on-nikon-z-cameras-with-full-autofocus/https://www.thephoblographer.com/2019/01/22/a-new-adapter-lets-you-use-e-mount-lenses-on-nikons-z6-z7-but-why/https://nikonrumors.com/2019/02/22/shoten-techart-tze-nikon-z-mount-to-sony-e-mount-adapter-mount-converter-to-be-officially-announced-next-week.aspx/
Physically it should be possible to do.... to adapt and E-mount lens for the Z-mount camera. 18mm to 16mm. 2mm is plenty of space for an adapter (there have been 1 and 1.5mm adapters in the past, for some other combos). Plus the Z-mount has a very large diameter to accommodate an adapter.
There may be some over-compensation in the dimensions they've chosen... Nikon has struggled a long time with their F-mount's diameter, as well as it's relatively long flange to film distance. Those have made it difficult for them design fast, super large aperture lenses, incorporate electronics and made it impractical for most other mounts to be adapted for use on Nikon F-mount cameras, but easy for F-mount lenses to be used on other manufacturers' cameras. Canon got blasted for abandoning their FD/FL mount in the late 1980s, replacing it with the much large diameter and shorter lens register EF mount... but that difficult decision has paid many dividends for them since then, including the ease of adapting many other system lenses for use on EOS cameras.
A bigger question will probably be to get the electronics of the lens and camera to talk to each other properly. Getting AF, aperture control and, if present, image stabilization all to work. Distance info, lens brand/model designation and other data may be less critical, but also may be important for some purposes (for example, modern flash may use distance info derived from the lens).
As noted... There already are adapters for Nikon F-mount (DSLR, 46.5mm register) to Z-mount (MILC, 16mm register). But, as also noted by others, there never will be adapters for the opposite. Optically it will be pretty much impossible to ever adapt a Z-mount lens for use on an F-mount camera (or any other DSLR mount, for that matter).
Be a little patient.... Z-mount has only been out for around for what... maybe 6 months now? Sony E-mount was introduced almost ten years ago and the Nikon F-mount has been around since 1959.... so there's been plenty of time for third parties to step up and design F-mount lens to E-mount camera adapters. It will just be a matter of time until there are lots of different adapters for Z-mount, too. There already are quite a few for vintage, purely mechanical lenses such as Leica M, Leica 39mm, Olympus OM, Canon FD/FL, yada, yada. There are even already some for more modern lenses, such as Canon EF to Z-mount... HOWEVER they don't support autofocus, image stabilization... or probably most importantly, aperture control. It's always the easier adapters... the ones without electronics.... that come to market first.