One explanation of the massive performance increase of the M1 is the SOC - cpu, memory and gpu all on one chip.
What will Apple do for the Pro systems on ARM? Adding the cores (28?) may be feasible on the SOC, but
1. How will they support up to 1.5 TB of memory?
2. How will they support the performance equivalent of 2 graphics cards, 64 GB each?
It seems that these will have to be separate modules.
Now there is a gap between the iMac and the Mac Pro with the iMac Pro high end configurations gone. I hope it doesn't take a year to fill the gap.