I suspect the reason Nikon is taking so long to release the Z9 is in order to perfect the AF so that it's comparable to Sony. After all that's really what they historically did better than others with DSLRs and are now behind with mirrorless.
Sadly there won't be a Nikon mirrorless in my future. When they changed the lens mount they opened the door to consider other options. My cabinet full of lenses is no longer an anchor. Nikon began to disappoint with the long delay of the D500, continued with QC issues on the D800 followed by delayed deliveries on multiple products that continue to plague them. Around the same time that I purchased the D800 that had to be returned for recall repairs I also purchased a 500mm f4G. It also had to have warranty work done due to being so far out of tune that max correction in either of three camera bodies could not correct it. How could it even make it out of the factory like that? Bottom line I've lost confidence in them as a company. This after spending tens of thousands on their "flagship" bodies and "exotic" lenses. They've gotten their last dollar from me.
Last week I spent several days shooting with a guy who had a Sony A7Riv/200-600mm. He is a total novice and was nailing focus every time from a moving boat. He also had a pretty high keeper rate on BIF which the A7 isn't really designed for. I was really impressed. I see an A1 in my future. And funded by the sale of my Nikon gear. I will be hanging on to my D850 and 500mm PF. Will have to pry them from my cold dead fingers.
Anyone still interested in some well cared for Nikon gear after that ringing endorsement can message me