You buy as you have a need. Don't wait for vaporware as sometimes you'll wait forever.
The Z8 is compelling in many ways, but it's larger and although the back display is a great improvement over the older Z II series, it's not enough to spark my interest with what I have and use. There's nothing that will make my final image any better.
I like some of the new features of the Z 6 III, especially the new articulated display, it's another iteration.
I just sold another bunch of images for a commercial installation, mostly larger prints, and not one file from a camera with more than 12-16 mp. Last month, one of the images was a 60x40 gallery-wrap canvas from an m43 camera.
Bottom line, with good craft, nearly any camera made in the past 10-15 years is fine for 95-99% of all photography. And even newer-model iPhones and similar are quite adequate for much of today's work.
If your work is heading to social media, a smartphone is plenty. If you are printing to hang on the wall, most digital cameras are fine, even in the 10-24 mp range. I even have a few pix from my iPhone hanging in my studio. It was the right camera for the occasion.
IMO coming from the days of film, even digital cameras from 20 years ago were an improvement and since that time continue to improve though not as quickly today.