I don't suspect an 8k iMac any time soon. If anything, they would go 6k so it matches the resolution of the XDR. And that would likely mean a 30" iMac.
And 2 screen sizes have been the norm for so many years I can barely remember the last time that there was only one (early 2002?).
For giggles, I just measured a 21.5" iMac and it is almost exactly 24" from bottom left of the black bezel to the curved upper right. If that was a tiny bit larger, and the curve diameter a tiny bit smaller, then a 24" iMac would fit neatly into something about the same size as the current 21.5". So, it seams fitting that the rumored 24" iMac is a replacement for the current 21.5" form factor. And that leaves a lot of room for the 27" to grow in both size and resolution. So, a 30" display could make a lot of sense, considering it wouldn't be any larger physically than the current 27.
A 24" 5k and a 30" 6k thus make very good sense, at least aesthetically.
But, my inner hunches tend toward the current screen sizes within new, iPad Pro-like bezels.
I'm drooling a lot, because that smaller screen size is my next Mac.
