My guess is the iMac Pro is a one-off, and they'll unify that once the iMac moves to ARM.
But also, yeah, the iMac design is really just several refinements of the 2005 iMac G5 design (replacing white plastic with aluminum, adding glass to the screen, adding Retina, decreasing the bezels and thickness, removing the optical drive, etc.), but I'm not sure there's a pressing need for a new design there. It's simply the new dependable mid-range desktop.
If anything, the last major rev that reduced the thickness was a misfire. It caused several unforced errors like making the RAM harder to replace, and making thermals worse. It's nice that they have the better cooling system in the iMac Pro, but is it really necessary? They could've simply left it a little thicker. Who looks at the side of a desktop display?
I do like products to look nice and perform well and I do sometimes just stare and admire well designed products lol.
The iMac needed to go back to the G4 flexible arm a long time ago for ergonomics and adjustability. The XDR display has essentially re adopted that mechanism but without the side movement.
In terms of the cooling, the iMac Pro design alleviated that so there was no need to thicken the case. Its just curious as to why it’s not in the standard iMac.