Steve, thank you for this 600PF video, I always enjoy watching your videos!
I followed the announcement with interest, because although I switched from the D500+500PF to the Sony A1+600GM, I now miss a "carry always and anywhere" combo, and a Nikon Z8+600mm PF lens would qualify, although I don't neccessarily crave a diminutive lens like the 500PF or current F6.3 Z600PF. I would not have minded the size and weight that a Z600mmPF would have had if it had been F5.6 at all, it would still have been nearly half of the Sony 600GM.
So the lens, however nice, does not really make me want to adopt a Nikon combo, that would b.t.w. cost a whopping €10.400,- where I live.
Anyway, that's my consideration, but I would like to point out, that your emulation of the (to be expected) bokeh of the Z600PF does not convince me at all that it would not have been better for the Z600PF to have been a F5.6 lens.
To begin with, you use a sample image where there is a subject, then a lot of empty space, and then a background. That is nice, but in such a case the OOF rendering of almost any lens would do (I still see a big difference myself between F5.6 and F6.3 btw.). What struck me the most when I switched from the 500PF to the 600GM, was the vastly improved "contextual" rendering, meaning the rendering when a subject is surrounded left, right and bottom by a background. Also, when a subject is fairly close to a background the OOF rendering of the 600GM is also much much better.
The other issue, that you touched upon, is that a lens with a narrow max aperture sucks at taking a crop, whereas the Sony 600GM can be cropped to 100%, and still render a pleasing background.
I have also found that lenses with a larger front element render images with better clarity and a better 3D feel. I did a comparison between the Sigma 500/4 and the 500PF when I had both, and set the Sigma to f5.6. The images still had a better 3D feel and better clarity.
I miss these considerations when you come to the conclusion that the difference between a 600mm f5.6 and a 600mm f6.3 lens is merely there on paper. Feel free to completely disagree with me, but I once had the Pentax DA560mm f5.6, with a 112mm front element, and that lens had such great clarity, I have been searching to replace its character ever since selling it (very poor AF and bad correction of CA) and only the 600GM has it beat on clarity of the images. Granted, the Pentax only has 6 elements so get's some extra help.
I feel Nikon missed a chance here to do something really special, and put the lens better in line with the 800PF, but no doubt there will be many happy owners for which a 1,5kg, 27cm 600mm lens is a dream.