After looking very hard at the Z8, I decided was not the solution for me. I will find my camera in an upcoming semi-Pro APS-C if it ever comes with new high resolution zooms. 30+ MP would be very nice. Or I may be well served with an Z7III and use the Full Frame for headshots, family reunions. When In the field, I need a lower weight and I will crop the hell out of my pictures to get A3 prints. I never print larger than A2. Then I will use denoise and upsampling. The Z8 is too heavy for me in the countryside, and the Z7II may get upgraded some time.
You face the neverending quandary. Even harder now the Z8 is out and seemingly more available than many thought -- I speak as an owner of 2 Z8 and 2 Z9. The Z8 is spectacularly good -- and provides 19.5mp in DX crop -- a perfect D500 replacement and so much more; but NOT the 26mp or 30mp DX that it appear many (including you) want.
Just a D500 replacement is not enough Nikon has to deliver more and more resolution but at what price?
Well we will have to wait to see which Body Nikon will release later this year.
If you buy a Z8 you will still have a fantastic camera in the Z8 -- quite possibly the best "not a flagship" body Nikon has ever produced -- so much better than my D850 and D500 were and certainly anything that came before them.
As I set out in an early post in this thread - I greatly doubt that a Z90 with 30+MP sensor and all the Expeed 7 goodness will be available for less than US$3,500 and it may be closer US$4,00 or possibly more. What makes the Z8/Z9 so special is the fastest sensor in user today; a sensor that to support dual channel data delivery that supports a blackout free EVF and an AF-system that refreshes every 1/120th second.
I simply do not see Nikon coming out with a Z90 that would NOT use a similar shutter free design to the Z8/Z9.
You mention 30+ MP -- well this may be possible today -- but not shutterless (well not that we know). AND as a result it will not perform like the Z8/Z9 and this is the quandary Nikon faces -- some folk want a 30+MP Z6iii; others a 60+MP Z7iii and then "finally" but not least those like you who want a 30=MP DX body, which is equivalent to a 70.3+MP full frame AND I simply do not see it. I also do not believe folk have fully understood the Diffraction Limitations such a very high pixel density imposes on its use. [Sony A7RV users are already facing DLA's at F/7 and this is impacting the benefits of such high resolution when used in combination with "the more affordable glass". Matt Irwin posted a video comparing a 45.7mp sensor with the Sony A7RV and YES he pushed it by closing down to f/16 - but the effects start to show at f/5.7 and are apparent at f/7.1 and quite noticeable at f/8.5 == which is one reason why Canon is alleged to be holding off on their ultra high res APS-C body -- since much of their most affordable long glass comes with very small apertures.
26mp DX gets 6k and performance like the Fuji H2S -- a seemingly great camera with a 26mp DX sized sensor in a small form factor. This is the equivalent of 61mp in FX and as a result already in wider use, but not on FX wirth a Z8/Z9 level stacked BSI CMOS sensor.
The Fuji X-H2 has a 39.8 MP DX sixed sensor - that is a 93.2MP Full-frame equivalent and diffraction is already reported as an issue at f/5.6. Does this matter well no if you are going to post uncropped images on social media -- but if you are going to crop in from a 39.8mp image to "say" 11mp then YES you will see an increasingly soft image as apertures f/5.6 and higher are used. A 33mp sensor is good upto f/6.3; a 26mp upto F/8 and so on.
Thom Hogan made the remark the competitor Nikon has to watch-out for i the DX space is Fuji -- not Canon or Sony. I agree. Nikon has better lenses and YES the 180/200 - 600 will drop sometime this year I am sure -- but what DX body.
Will Nikon update the Z50 (yes); will Nikon drop a Z70 or Z80 higher resolution but slower fps and reduced AF Dx body possibly -- would such a body respond to the D500 replacement HAWKS who demand a Z9/Z8 in DX and very very high MP and performance --- NO.
So - for me I see the FX line up being refreshed and potentially expanded with a Zf -- so that is a Z6iii (30mp); a Z7iii (60mp) and a Z5ii (24mp) all wirth flow down of Expeed 7 (lite) goodness. BEFORE a super high resolution super fast DX pro dody is launched. AND therefore as a result my guess is you would be safe with a Z8 for quite sometime.
BUT Nikon has been really strong with its NDAs and keeping everyone -- particularly Peter in Nikon Rumours in the dark -- and that is a good thing unless you want to save your money for a not yet even rumoured body to emerge and then it does.