Apple's thought processes seem to be divided (interntally) into two camps:
1) iMac and Mac Pro;
2) Mac Mini and Mac Studio.
Camp 1 thinks having the best looking, high priced (compared to the, albeit uglier and not as well integrated) machine is the goal;
The Mac Pro is basically groupled with the Mini and Mac Studio. All three are systems would very much like you to buy an XDR display to work with.
The two camps in Apple are more likely:
1. "Green" ( bundled screens should be avoided on non laptops... very similar stuff the xMac folks grumbled about for over a decade. )
2. "Max Perf/Watt" ( on package RAM to lower power overhead. on package SSD controller to lower power overhead. on package GPU to lower power overhead , etc etc. etc. )
The iMac 24" shape in part comes from the fact they are laser focused on #2. They are putting plain Mn's into iPad Pros and iMac gets just as thin. The thin leads to less weight which is a "Green" offset since it has lower carbon impact to transport ( and store/inventory ).
Camp 2 thinks that modularity and maximizing capability per $ is important.
I do not believe the iMac should be killed. The Mac Pro needs a rethink.
The Mac Pro is a 'Mac'. In the modern era , the RAM , iGPU etc are what they are for all Macs. I think folks wishing the Mac Pro to go off on some Threadripper/Xeon W 'killer' tangent are fooling themselves. There is no financial rational motivation there for Apple to fork off that far in that direction for a very , very relatively low volume product all by itself.
The iMac 24" probably won't get killed. As long as M4 , M5 , M6 , etc get progressive improvements the performance zone that the iMac 24" will cover will grow over time. There are 'student lab' and other settings where the all-in-one device is just easier to secure.
Not switching out Lightning for USB on the accessories is really telling.
Not any more telling that a '1 year later' Pencil for the iPad 10th generation. They aren't executing and/or it isn't a priority. It is also cheaper for them ( bill of materials costs). The fact that the EU is forcing them to switch rather than a situation where they were internally motivated to switch , makes it not surprising at all they are dragging their feet where they can.
Apple moved the iMac 24" to USB-C so they don't really have to do much there. The EU statues allow 'old' products to keep on shipping ... so if they don't change the mouse/trackpad/keyboard then don't have to move to USB-C. In the mean time the giant pile of USB-C to Lighting cable providers can keep selling product (including Apple).
It says to me that Apple themselves were not planning to update the current iMac.
That is a huge stretch. The chassis of the MBP 14"/16" didn't really change at all either. The Mini is still the same basic form factor as it was in the Intel era. etc. etc.
More so says that Apple doesn't send large amount of Mac stuff through the Design group at any one time. If Apple makes large changes to Mac X then Mac Y doesn't move.
That Mac Book Pro laptops are obviously the big push, and the iMac is now looking like a legacy line that Apple's chief monks have yet chart the next path.
Apple has charted a path. The main problem is that Apple's path when it comes to screen tech is usually glacially slow. Apple's discrete docking-station monitors are sold for more than several years at a time with no changes. As much as an iMac adopts a 'blessed' screen tech by Apple , it is also assuming that "long time no changes" constraint also.
When Apple does a major change in screen tech then the iMac might change. Until then , same old chassis with same old screen.