I do expect a Firmware 2.0 update for the Z6ii and Z7ii cameras. I don't know that the cameras today fully realize the value possible using technology pioneered in the Z9, but there will certainly be hardware and power limitations in the Z6ii/Z7ii.
I'm not sure how closely you have looked, but each of the recent firmware updates has noticeably improved AF performance. Not all of that improvement applies to birds in flight, but there are some clear improvements. The big jump will likely be with version 2.0 - assuming there is such a thing. I can tell you that I know a future firmware update is being tested already.
For the longest time I used DX Nikon DSLR cameras for my hobby photography that included mostly travel, landscape and wildlife work. I did not often make images of fast-moving animals or birds, so BIF capabilities was never a pressing need for me, and for that reason I never purchased the more pro-like DX bodies. I started with Nikon D70S, then D90, D7000, and lastly D7500. I made great images with all of them. I always longed for the better IQ in the FX sensors but I did not like the size and weight associated with those bodies. That all changed when Nikon launched the Z mirrorless cameras. Here suddenly was an FX sensor in a body that's smaller and lighter than the D7500. I made the switch to the Z6 at that point.
I found the Z6 more or less on par or even slightly weaker than the D7500 in terms of focus tracking of faster-moving animals. The Z6 lost focus more often on flying birds. Subsequent firmware updates certainly improved the focus tracking and focus stickiness of the Z6. It was during this time that the Sony mirrorless cameras became famous for their ability to track fast-flying birds. With this technology becoming available it woke in me a new photographic desire, that of BIF. BIF has now become an integral part of the kind of photography that I do for a hobby. The big problem here is that the Z6/7 series cannot compare with Sony's offerings for subject tracking. Granted, the Sony cameras are also more expensive.
So here I was with a full frame Nikon Z6 that was inadequate for doing serious BIF work and that resulted in frustration. I therefore immediately changed the Z6 for a Z6II as soon as it launched. I expected (like may others I'm sure) that poor BIF focus tracking would be significantly improved with the addition of the second Expeed 6 processor. That did not happen and the Z6II still cannot do for my BIF work what I need it to do. Focus did improve with the Z6II, but certainly not as much as we would have expected from the addition of a second processor.
I guess I have to agree with some folks who say the Z6/7 series was never marketed as a serious action camera, so in the absence of any promises from Nikon about action work it really means we have to take what they give us in these cameras. There is one thing that stands out for me about the focus capabilities of the Z6II: The included subject tracking feature is largely useless and a great disappointment. I have tried using it many times on flying birds and airplanes. Any clouds or other objects in the background cause the camera to lose the subject. For that I will criticize Nikon. As poor as this feature is they could just as well not have included it.
So Eric, considering what you're saying about an imminent firmware upgrade for the ZII cameras, I'll be pretty satisfied if Nikon can make that subject tracking feature perform as well as what we have a right to expect. Either that, or replace it with a better subject tracking mode altogether.
I'm waiting, but at the same time I don't want to wear out my camera before Nikon launches that upgrade. Because I now
want to do BIF work going forward, I'll need those capabilities in the near future. I don't need the capabilities of a Z9, but I do need better than what I have now.