Besides and beyond cameras, Lenses are as important if not more so: especially as we have so much choice across the Greater Nikon Ecosystem. The Z Nikkors are all solid investments, with the best in this mount rated best in class. This is the consensus, (
see links), and includes at least 2 reviews of the 50 f1.2S: rated
Excellent and
Again, "...
most impressive 50mm prime I’ve ever reviewed", and a
fourth. These reviewers cannot all be dishonest, surely. This consensus has extended recently to the 3 new Z telephotos (100-400 S, 400 TC, 800 PF). The Z-Teleconverters are also significantly better optics. Cost is the crux for many of us. The FTZ solves many challenges, at least with AFS glass.
There's the fundamental rule of growing a camera system that hasn't changed in decades - 'Marry the Glass, date the bodies',
attributed to photographer David Hobby of
Strobist fame, it's a one-way door investing in a Z-mount optic: eg the 800 PF but I've no doubts now it's worth the leap. Overall, it's hard not to justify investing in at least 1 PF Nikkor - of which there will soon be 4. In their own niches, each PF Nikkor is a game changer. The practicality is I carry on with a Nikon mixed system, mostly F Nikkors interchangeable across 2 DSLRs and the Z9. I have added a Z UWide, medium zoom (24-120 F4S), and recently 800 PF with both ZTC's. And it's going to be intriguing to watch how Nikon proceeds to roll out Z9 technology across its Z cameras...
In summary, my D850 has worked hard, in it's fifth year. It's pointless to trade in such a reliable camera, with key Mirrorless features in Lview. Both D* flagships keep on delivering.... especially if (1) the subject falls within AF sensor coverage, and (2) adhering to the rule of minimal cropping. Thus I keep the D5 because as we know very well, it's unmatched in keys situations: knowing it will will deliver superb IQ at ISO12800 is reassuring to put it mildly. Nothing's changed since 2016, besides the Z6 sensor creeping up towards the uniqueness of a 20mp sensor, where the D5 and D6 keep their crowns for image quality in lowlight - underscored by their AF engines. In comparison, I try and keep the D850 and Z9 under 3200, the lower the better; 6400 is the cap I set striving for correct exposures (these thresholds were 1600 / 3200 with the D500). As for AFC, the DSLRs rarely grab backgrounds, so +1,
but I've concluded the Z9 AF has so many advantages: not least 3D AF mode, and it now has the Custom Area modes analogous to the D6 and RSF Hold etc.
<Edit> Compared against the industry's best DSLRs....
So after 2+ months 'Hands On'. I've concluded the Z9 meets my priority needs + more