A very interesting discussion. Personally, the FTZ adapter that I think Nikon (or someone else) should make is one that supports AI metering. If the lens data has been set into the camera, an AI FTZ adaptor would allow the lens aperture to show in the viewfinder and to be recorded in EXIF data. I think that would be a very useful and desirable feature. I am sure there are plenty of photographers with legacy AI, AIS, and old AF lenses (including AF lenses which don't AF any more) who still like to use them on their Z cameras. The current lack of viewfinder information means you would constantly have to take your eye away from the viewfinder and over the top of the camera to see if the aperture has been set correctly, or turn the aperture ring to max and then count the clicks until the required aperture has been set, which slows down the picture taking process. This could mean you risk shoot at the wrong aperture or lose the shot. Having the shooting aperture in the EXIF data is also useful when reviewing images later.
An AI FTZ adapter would be much simpler and more robust than one which supports screwdrive AF, although more complex than the current adaptor. Not having AF with legacy lenses would not bother me so much as Z cameras have good tools such as focus peaking, increasing magnification, and IBIS which allow the photographer to focus quickly and accurately.