Got my hands on a Z8 for the first time yesterday and.... well.... not quite what I was expecting! I've been lusting after the Z8 since it came out, and am seriously looking at it as a replacement for my Z7. I knew it was going to be bigger than my Z7 / Z5, but was surprised quite how big and bulky - it felt a lot more like my old D810 than it does to my 2 existing Z bodies. and I'm not sure I liked that.... I didn't get a chance to switch it on or put a lens on it (
LCE very conscious of how hard they are to get hold of and how quickly it was likely to sell, so didn't want it to be used at all) so this was based purely on feel. Next time I'm in town (September) then hopefully they'll have more than 1 in stock and I can have a proper play - I'm sure that'll change my mind a bit....
However I went Z for 2 reasons - the main one being to get my camera and lens weights down (I take both colour and infrared bodies plus appropriate lenses everywhere). In my head, I felt like I'd be OK with a little bit of extra weight and bulk, but in practice, now I'm not so sure!!
I did see a rumour of a Z7III with an 80 or 90-odd mp sensor, but also saw that rumour being talked down as the general consensus was that the Z8 probably replaced the Z7 line. I can't help thinking a Z7III type body is probably the camera I'm looking for (landscapes mostly) but have to date purposely overlooked the Z7II as just too similar to the Z7 to be worth the upgrade.
So I'm a bit lost in how to relieve my Nikon shaped GAS now!

(well other than a 20mm F1.8 for astro and a 28-400, which is apparently the holy grail do everything infrared lens I've been looking for)
I've suggested this before, but I wouldn't read too much in what Nikon have done in the last few years, because it's only now that they are settling into what looks like a long term model structure. You have seen this before with Nikon. when they "sort of" used the D7xxx range as an interim model for the never produced D400.
My thoughts are that both the Z9 and Z8 are underpriced at the moment, but needed to be, because the Z6/Z7 range didn't compete with Canon and Sony for AF, and Nikon desperately needed Pro level mirrorless replacements for the D6/D850. At the moment the Z8 is bridging the Pro and ProAm space to compete with both the Sony A1 and A7, when really it should only be competing with the Sony A1. As a gripless Z9.
As Nikon get their model structure together. (there are currently three new models registered in China) I expect to see a Z8II and a Z9II with big price increases, which will leave a gap for a higher res Z7III to compete directly with the sony A7 series (size, spec and cost).
But, I also think that in the short term, we will see a Z9II (to compete with Canon R1) before the Z8II, and that the Z8 will stay as a Z7III substitute for a while yet. For me it would make sense for NIkon to release a Z8II and Z7III at the same time.
Having said that, I think the full retail price for the Z8 is still £4000, so there still seems room for a Z7III coming in at around £3000, which feels about right at £400 more than the Z6III. That would also seem to work for Nikon, as it gives a more direct competitor for the A7 satisfies those who feel the Z8 is too big, and it allows Z8 sales to slowly run down, in preparation for a Z8II.
My guess is that will only be a 60mp sensor, maybe a little higher. Nikon have apparently dismissed a very high resolution sensor because of diffraction issues ie they say a 100mp (36mm x 24mm) sensor is diffraction limited at around f4 and don't see that as a workable limitation.
Finally, these are obviously, just my idle thoughts on this, but I feel we need to just wait and see. I also wonder if the same people who are saying the Z8 is the Z7III are the ones who insisted the Z7 was the D850 replacement, when it clearly wasn't..
I like the size of my Z8, and currently, my first choice of a backup Nikon body would be a Zf, It's obviously the first of the Nikon "3rd generation" full frame mirrorless bodies, and doesn't overlap with a future second Z8 body, or maybe Z7III body.