"I believe that to get D850 owners to switch to a Z7 III or Z8 replacement, the mirrorless replacement has to offer substantial advantages over the D850 because of the angst over switching lenses."
I'm not sure that's the biggest issue. I get an awful lot of response from site readers saying they "simply won't switch from an optical finder."
Over the years, I've encountered a lot of built-in and not-necessarily-based-in-reality biases from readers. For instance, the notion that plastic materials are worse than metal, that factories in China produce worse quality products than ones in Japan, that primes are always better than zooms, and the one that's relevant here: optical viewfinders are better than video screens (I'm using the typical pejorative wording I tend to get here).
Frankly, other than being able to see through the lens with the camera off, I personally don't see a lot of advantage to optical viewfinder. Perhaps I've been looking at "video screens" for too long (way back to the early 70's with television field cameras).
In theory, an EVF can provide a lot of things that are tough to do with an optical viewfinder (though we don't always get those added features; for instance, when photographing red flowers in macro with the Zfc recently, I couldn't find the red focus sensor box, so why can't I change the color of it?).
I do think, however, that you're hitting on one of the bigger issues, though. Moreover, there's more lens angst among the DSLR users than most might think. As I and others have discovered, the Z-mount lenses are better than the equivalent F-mount lens. So the angst is fueled by the "I probably should replace my lens set" just as much as it is by "I don't like using adapters", "the FTZ adapter doesn't work with my current lens", and "I'll eventually have to start buying new lenses and they won't work with my DSLR if I keep it as backup."
"The full frame Z’s don’t seem to bring enough to the table to justify the cost of transition."
This is related to the previous question, but has some additional hallways to explore. I've been vocal in lamenting that Nikon chose not to bring the AF-On+AF-area mode key combo over to the high-end Z's, but there are plenty of other bits and pieces that come into play, too. One obvious one is that Nikon hasn't added pixel-shift capabilities using their on-sensor VR.
We're still very early in the Z System (less than three years in our hands), which seems to get forgotten a lot. It was always going to be a longer haul before we got to complete parity with DSLRs in terms of everything (features, performance, accessories, lens set, etc.), as Nikon doesn't have infinite resources but needs to completely replicate a system that at one time had nine camera bodies and 65+ lenses.
As critical as some think I've been of Nikon, I give them good marks for what they've managed to do so far. But that's not yet enough to swing as many of the DSLR user base as Nikon needs to convert. Moreover, the timing is just terrible. Four of Nikon's Z bodies and 10 of the lenses have been launched into the pandemic-damaged economy. The on-going issues with supply chain and more with the pandemic have made Nikon look slower to act recently than the user base is demanding.
The Z9 is probably our first new chance to see just how much effort Nikon is putting into the Z System and how many of the small bits and pieces that they've tied up and gotten right. So I hold out hope that it's just newness to the market and a very bad external factor that have us where we are today and are keeping the transition from going more smoothly.
But notice the word "cost" in this reader's comment. I'm getting that echoed by more and more in the DSLR holdouts. It's not just the perception of little benefit/capabilities/performance that's keeping the D500, D850, and D6 user away, it's the cost. That's a tricky one to fix. My advice to Nikon is to figure out more bundled set and trade-in options to help defray some of that cost perception problem.
"As you said, it's the lenses that are the issue for me when thinking about the Z9. Like you, I find the idea of using the FTZ on the 400/2.8 unappealing, especially with a TC. And I'd at least have to get the Z 70-200/2.8 in any case. So it is, financially, quite a bit to swallow. And what would the second body be? One of the DSLRs? Meaning I have to hold on to quite a few of my F-mount lenses and do the mental gymnastics of switching between AF systems each time I grab a different body? Not too attractive a thought, frankly."
Complete system transitions are tough. Cost, time, setup, training, all come into play. Since I'm already personally dealing with quite a few professional photographers who are wondering what the Z9 means to their DSLR gear closet, I expect to be dealing with the transition questions for quite some time, and they'll intensify once details start becoming more clear.
It's the ones that straddle (continue to use a D5/D6 DSLR but pick up a Z9) that I worry about most, and for the reasons you suggest. A complete sports pro swap from DSLR to Z System is probably US$34,000+ (two Z9 bodies, f/2.8 lens trio, 400mm f/2.8, some other odds and ends) less what you can get for the older same/similar DSLR gear. That's out of the realm of possible for most of the pros I've been talking to about possible transition strategies, and it doesn't get better picking Canon or Sony as your new platform. So the temptation to straddle and slowly transition is high, and it will be a bumpy ride (and bumpier still if you pick non-Nikon for mirrorless). My advice to Nikon is to come up with a lease/purchase program for complete switchers (in addition to the trade-in options I already mentioned). Not a perfect solution, but Nikon needs to come up with as many ways to nudge the pros to move as possible. Either that or Nikon needs to verify and prove that the high-end DSLRs still have four+ more years of life to them through upgrades and support (including new lenses).
"In a few weeks time, I am going on my first trip after not going anywhere for 18 months. To prepare for it, I bought... precisely nothing from Nikon. The only things I have purchased are some accessories for my tripod (a leveling head and panoramic stop), and some clip-in filters (from Kase - and thanks for pointing those out in one of your product articles!). Nikon got none of even that minimal revenue.
I would have loved to replace my 70-200mm/4+FTZ combo with something new. And if there had been a new pancake lens or two available, I might have also opted to not bring the 24-70mm and go with a compact 28mm and 50mm combo. But none of this is available, and so Nikon got no revenue from me.
Am I happy with what I have? Will I be able to take photos and enjoy myself? Of course and of course! But my enjoyment does not bring Nikon any new revenue or profit."
The recent paucity of new lenses, in particular, has a lot of Z System users like yourself on credit card holiday at the moment. I get plenty of folk writing to me about "too bad the 100-400mm or 200-600mm wasn't available for my travel this year."
As I noted above, Nikon got caught in some very bad timing. I'm pretty sure that the compact lenses you wanted and the telephotos others wanted would have been available by now if COVID-19 hadn't caused havoc with Nikon's plans. There's plenty of pent-up demand in the camera/lens arena right now across all brands, and every manufacturer has several products that can't be delivered to demand at the moment. I give Nikon a "pass" on this one, with the exception of messaging. There's near zero messaging here from NikonUSA. In Japan, there's been a string of "out of stock, can't deliver now" type messages, but with no details or even a suggestion that Nikon will address the problem or when (is it just out of stock for the time being, or is it discontinued?).
"It seems these days that the feature du jour for mirrorless cameras is the autofocus system; how good will it track the eyes of a person, a wild animal, or the pet dog. Of course Sony and Canon mirrorless AF systems are out performing Nikon right now, and it seems long-time Nikon action-shooters have been abandoning ship. This is worrisome.
Why is it so hard for Nikon to come up with mirrorless AF performance similar to Sony or Canon? Why can't Nikon take the "guts" out of their successful D4/D5/D6 AF modules and repackage it to fit into a mirrorless camera? Easy-peasy, right?!"
Let's start with the latter, first. DSLRs have an advantage over mirrorless cameras in that they have dedicated AF hardware (sensors) that are large, multi-directional, and fast. But that part sits behind two mirrors. There's no way to use it in a mirrorless camera.
So let's get to your first paragraph. I don't particularly agree with your contention. As I'll continue to write, Nikon's Z System autofocus is quite good, and many will find it better than their DSLRs. In the firmware updates and the II models Nikon brought the system pretty close to state-of-the-art, and arguably as good as the current Sony A7 Mark III, for example. So what's wrong is not the autofocus system, it's the messaging. All the YouTube and influencer exclamations exalting Sony's focus is out-weighing the reality.
Moreover, there's apples versus oranges confusion going on all the time in the Interweb's various proclamations. The Sony A1, for example, is indeed really good, about as good as my Nikon D6. But the Sony A7 Mark III is an older camera and not nearly as good. While that model seems to autofocus fast it often doesn't do so precisely when tracking moving objects. Does Sony get dinged for that? No. But Nikon, who matches or exceeds it, does.
Are there things I want to see Nikon improve? Absolutely. Are they being out-performed in any truly meaningful way for most of the camera users? No. I suspect that we'll see another wave of some sort of shouting about autofocus when the Z9 launches. Hard to predict whether all the incentivized influencers will try to say that Nikon failed or whether they'll suddenly be shouting hallelujahs. We'll see. But as always, I prefer learning and testing before saying anything. I'll once again point out that even in late 2018 and early 2019 without the firmware updates to the original cameras I was able to get great sports and wildlife results from the original Z6 and Z7 and firmware when everyone else was telling me that my camera would fail miserably at that.
That other photographers couldn't seem to get their Nikon Z cameras to focus for them says more about those photographers and how much energy they put into learning a new system more than failure on Nikon's part. Again, though, are there things Nikon can improve that would make me happier? Absolutely, and I've been repeatedly vocal about what they are.
