Yesterday at some Chinese social network where people shares tech "speculations" someone with good record posted the following for a while and then deleted (take with huge grain of salt):
Apple readies Mac mini and iMac, iMac Pro full re-new , new aesthetic follows Mac pro and Pro display.
CPU, AMD based "hybrid" processors (custom Ryzen/Threadripper).
Base iMac 21/Mac mini to share APUs Ryzen 4000 series based, iMac 5k 8-16 cores Ryzen 3000 aeries - Navi GPU s (the gaming iMac), iMac Pro 6k Threadripper 24-64 cores Navi 21, pcie4 everything.
Hybrid processors, could mean the management controller likely build around or deeply integrated into T3 SCM.
IMac Pro more expensive, should start at 6000$, all other Macs to keep current base price.
Basically that's just what's speculations/hopefully tells everywhere, nothing unpredictable except for the "hybrid" CPU, while a custom Zen3 Chip is easy bet (in an all AMD Mac ) that hybrid word IMHO means Apple replace Zen Bridge Chip (10nm) with something based on it's (arm) T3 7nm, likely integrating RAM encryption (which comes sense) and more power efficiency and no chance for DIY cheap upgrades, unless you buy an Apple baked Ryzen CPU.
Keep track on this rumor, being true will be the most attractive iMac line ever, also the new aesthetic improves the crappy iMac thermal envelope, no throttling, no Intel bug's, pcie4.
I would buy that 6K iMac Pro with closed eyes even at baseline configurations (24 core, wx5700 likely) should be a huge upgrade on current iMac Pro (and a Mac pro sales predator).
A Mac mini with a cheese grater front/rear grille plus on top power/tb3 ports like the Mac pro will sell very fast too