As noted by many the use case for owning/using the Z9 over the Z8 is clear -- well at least to me and the pros I know.
Demand for the Z9 for sports, action, wildlife (so long tele users and those of us who want built in GPS, 2 matching card slots, the best robust weather sealed bodies and large batteries) and fashion/portraits who often shot in portrait and studio shooter who want a sync port. AND for folk who want over 2 hour record times. I cannot see many sport shooters who shoot remote relying on a dongle to stay plugged in when there is an option with a built in ethernet port and a large battery -- basically NX Field users
Whereas the Z8 is smaller and allows direct power to be fed into a rig/set-up.
I am hoping within a month I will have 2 of each Z9 and Z8 in my studio.
What will make me sell my two Z9? -- nothing planned until Nikon comes out with a successor flagship in a while.
One wonders whether Nikon will issue an updated Z9ii body for Paris Olympics or wait for the North American world cup in 2026. My hope is that it will be the 2026 WC leaving Nikon lots of time to upgrade the firmware in the current model.
The Nikon press release for the Z8 was clear -- it was launched with planned firmware updates in train -- "Upcoming features will be added in planned firmware updates, including an Auto Capture function, which will allow a photographer to automatically trigger a remote camera on user-set parameters. An update will also allow for the base ISO to be extended down to 200 when shooting video footage with N-Log enabled."
Hidden (well to me at least) gems are still emerging in the Z8 -- like Fast-AF-ON for video - "To speed up your workflow when repeatedly shooting different takes of the same scene, Fast AF-ON lets you quickly move the focus back to where you had it at the start of the shot when resetting, simply by pressing the custom buttons you have assigned for this function. You can also choose the speed at which the camera shifts focus in a range from -5 to +5."
-- more data will emerge as more folk get to grips with the Z8 and documentation is available to download. An English version of the brochure can be downloaded here
-- I expect we will see updates to the Z9 to level it up to the Z8 and these changes to both the Z8 and Z9 soon.
Many are still hoping for pixel shifting multi-shot hi-res, false colour for vid, and then the unlocking of 30 fps RAW and so on.....
This leaves Nikon plenty of space to update the Z6ii, Z7ii and Z5 -- all of which will happen. Clearly not soon enough for many.
I am still doubtful if Nikon will issue a ProBody Dx and if they did I expect a price of 3,500-4,000 if it uses a Z8/Z9 style sensor -- otherwise the Z50 is the direct replacement for the D500 -- but obviously not with a 30+MP sensors nor Z9/Z8 AF or Video.