As many know ime shooting mirrorless due to the need to lighten my load,Nikon mirrorless fX was never going to be a contender for me but i am disappointed that Nikon has been so stupid (IMO).They have put themselves behind Sony and ime sure Canon is laughing all the way to the bank now Nikon have shown them what not to do.
Smaller and lighter gear is a valid goal. For me it isn't relevant though, all I want is a better camera. That would mean higher frame rate due to less mechanical moving parts, better autofocus due to wider AF point spread, and easier focusing with MF lenses due to zooming viewfinder with focus peaking. Also I am interested in exotic, wide aperture lenses that the Z-mount would allow. The first gen Z-series isn't there yet for me, but these aren't top of the line models either, these are midrange/entry level cameras. I only shoot stills, therefore progress in video features is not enough as I am not interested at all. Since the f/1.2 or f/0.95 lenses are not ready yet, the Z-line currently is not a better camera for me.
I do not want a smaller camera than a D5 since hand holding an AF-S 200/2VR2 or AF-S 300/2.8VR or AF-S 400/2.8VR with my daughter's D3200 is impossible, I've tried it. But it is easy with a D4S or D5 and I do it every week worth 3000-4000 pictures. If small cameras are all Nikon will do in the future my money stays in the bank. I have enough gear to last me a couple lifetimes.
The fact that current Nikon Z-series is behind current Sony III series is just a testament to the fact that camera development takes years. When Nikon began the Z-series design they aimed to make a better camera than Sony A7 II (or the II series) and they succeeded in that, imho. Unfortunately for Nikon Sony moved the goalposts with the III series, a lot!
I'll have another look at the mirrorless business when 58/0.95, 35/1.2 and 50/1.2 come out along with a Z8 and a full-size (D5 form factor) Z1 (or whatever) that can hold a lot of batteries.