Most people are focusing on the upcoming Z9 as the product that "solves" Nikon's Z System issues. Nope. Most of the Z9 hope is that Nikon takes all the rough edges off the Z6/Z7 model lines and does a leapfrog of Sony with some new technology. And that this then solves all Nikon's customer problems.
It does not.
Not even close.
I'll put things in a personal context: I'm rethinking my lens closet at the moment as there are a lot of lenses I find that I'm not using much as my work has shifted a bit and I'm seeing some interesting and perhaps better choices pop up. I've decided to sell my 500mm f/4G, for example, as at that focal length the 500mm f/5.6E PF is perfectly fine for me. I suspect that a 120-300mm f/2.8E would fit very nicely into my needs at the moment (as do many other pros I talk with), and I'd probably give up my 200mm f/2 if I bought that lens. The problem is that the 120-300mm is a US$9500 lens in a mount I'll probably be leaving. As a customer with a budget, I can't completely justify a half-mirrorless, half-DSLR lens closet. I doubt I could depreciate the lens properly to my costs, because it's on a mount that Nikon—due partly to Nikon's terrible and non-existent messaging—seems to be abandoning. Two of my sports photographer buddies want that 120-300mm (one has already bought it and is about to deploy it), but that leads them to believe they'll stick with a D6 and not opt for a Z9.
In other words, We need to know that DSLRs are going to continue to iterate and keep up techwise—particularly the D500, D850, and D6—or we need a better solution than an FTZ adapter to justify buying such an expensive lens. Sticking DSLR lenses onto a Z9 with an adapter isn't a solution I or other pros who would be interested in the Z9 wants.
Why not? Well, besides the financial implications of mount switching: (1) we have long experience with TCs that give us enough droop problems on the long exotics that we sometimes lose mount communications (hey Nikon, still fighting gravity are you?); (2) adapters/additional mounts can produce AF Fine-tuning needs, even on a mirrorless camera; (3) the FTZ has that built-in tripod mount that just adds complications and sometimes incompatibilities to how we want to mount things; and (4) most of us have noticed a very slight delay in autofocus tracking with a fast exotic on the FTZ and thus worry that we won't get the performance we paid for. The list is probably longer than that. But the point is that there's a mismatch going on that has us hesitating to open our wallets. A Z9 by itself doesn't really change anything. (This is one reason why I say that Nikon needs a mount conversion approach for at least some of the exotics.)
And again, I'm not alone in this thinking. Quite a few Nikon-using pros I've been talking to are going through the same angst. Any transition triggered by the Z9 would be problematic on the lens front unless all you need is 14-200mm. Yes, a 400mm f/2.8 with a built-in 1.4x teleconverter would be a nice addition, but that's likely going to be a US$12,000 lens, and it won't play on our remaining DSLRs, so we'd need to hold onto our existing F-mount lenses. Yikes.
Thus, to transition my work fully to mirrorless, I have to think about giving up the DSLRs and their lenses pretty much completely, and then going with a far leaner lens closet (14-24mm f/2.8 S, 24-70mm f/2.8 S, 70-200mm f/2.8 S, 400mm f/2.8 S that's also a 500mm f/4). I could certainly do that, but I'd lose flexibility. Ironically, I'd have more flexibility sticking with the D500/D850/D6. And more and more folk I've been communicating with are coming to the same conclusion.
For many of you reading this, this may be good news. If pros are hesitant to opt for a Z9 when its announced later this year, there will be more to go around to the enthusiasts who have the disposable cash to just buy "best in breed."
The other good news is that Sony isn't exactly in the position to easily pick off those same Nikon DSLR pros. Beyond that 14-200mm range, the A1 pro buyer really only has the 400mm f/2.8 and 600mm f/4 to choose from (though the 100-400mm f/4.5-5.6GM and the 200-600mm f/5.6-6.3G are already out, while Nikon's versions of those lenses are still just on the Road Map).
Still, my point remains: no matter how good the Z9 body is, it doesn't solve Nikon's problems with professionals. Time should heal all wounds here, but every year there's a group of pros who are on their planned upgrade/enhance timing cycle, and those that are contemplating big gear investments for the next two-to-four year period are going to have to hope Nikon delivers far more than a great Z9.
Bonus: To some degree the truly serious D500 and D850 owners have similar dilemmas. Were Nikon to make a Z90, for example, the problem would still be lenses: Nikon would almost certainly lean on the FTZ adapter for the group that would buy a Z90 because the appropriate Z DX lenses just don't exist, and likely won't for some time. D850 owners might have an easier time justifying a Z7 III or Z8 replacement, but I'm willing to bet a number of them would be agonizing over lenses.
