New Nikon Z9 flagship?

That's a good description of the tradeoffs camera companies face.

High resolution sensors present several challenges. There are huge files with lots of data. All that data needs to be read from the sensor and then processed. That takes more time. It also increases the issues with rolling shutter. The resulting large files take more time to write each file to the card, so if you have fast frame rates, you need a very large buffer or it fills in 3-5 seconds. Uncompressed files increases speed but limits quantity. The problem is compounded in the Sony lineup because the memory cards are exceptionally slow - SD UHS-II - which has a write speed of 150 MB/s in cameras. And that means it takes a long time to clear a buffer and free up space for another burst. Depending on the processor, you also face decisions about how much processing power is directed to processing and how much is directed to AF.

All this means you can make action cameras or high resolution cameras, but there are big compromises for each approach. I don't see that as bad - just different. I expect to see more of a split on the Z6ii and Z7ii between these two strategies. Something innovative would be to allow a mode setting to let you choose between high resolution or speed, and then direct the sensor and processor in a different manner.

If you have a Z7ii, why would you really need something else for high resolution? Focus accuracy is more important with higher resolution, but it could be slightly slower.

The proposed Z9 still seems a little confusing about whether it's an action camera or high resolution camera. Clearly it's a pro body. Maybe longer term Nikon will have a Z8/Z9 combination to provide both types of cameras in pro bodies. They just released a D6, so the action camera is covered for now. A Z9 for high resolution, followed by a Z8 for pro body standard resolution and fast action, could make a lot of sense. That also allows some time for lens development, spreads out the release cycle to reduce shortages, and could balance the engineering work over a longer time period.