There is no question about there one day will be a Nikon with a global sensor because the tech is now available, but the question is, is it a must have?
My answer? No. The primary benefits come at extreme uses. And as you pointed out in other parts of your post, there are compromises. One such compromise is the implied smaller electron well capacity due to the base ISO of 250.
Nikon has shown their own global shutter work well over a year ago, and has several patents in the area. The "how quick" question is answered by my comment above: for a high-end, specialized product, perhaps more quickly now that Sony has made their move. But for the Z6 type of camera you were commenting on, I don't see the need. Just increasing bandwidth enough to forego a mechanical shutter is enough, I'd judge (which is what they did with the Z8/Z9).
Should Nikon make a camera with a global shutter its first priority or should they just make a new model line for people that might need it?
An improved Z6 III is the model Nikon most needs in their lineup at this point. The Z9 can still be improved via firmware (e.g. Nikon showed CAI on a Z9 quite some time ago at an Adobe conference, but hasn't released it yet).
The definition of what a Z6 III needs to be has now changed with the release of the Zf. More speed (perhaps a drop of the shutter) and perhaps more pixels seem to be the main things that would bring it back into being fully competitive.
What is the Nikon community wishes?
From my polling: Z6 III, 60mp+ camera, and Z70/Z90 speed DX camera.
From my own personal opinion, Z6 III is urgent, Z50 II and Z90 are getting urgent, and
some day a higher resolution camera. Add perhaps a mild update to the Z9 (e.g. the Z9s type of update).
