If Gurman is correct that the M2 will be 4nm, I would expect the M2 to be based on the upcoming A16 rather than A15 as has been assumed. If I recall the A15 used an improved 5mn process and the A16 will be the first to jump to 4nm. If I had to guess, Apple plans to refresh each Mac in about a 2 year cycle and each iteration of the M-series SoC's would be based on every other generation of A-series SoC.
I'm really confused about his comment about the iMac Pro as Apple stated pretty clearly that the Mac Pro is the only remaining Mac that needs to transition. Unless they have an Intel iMac Pro forthcoming? But that makes zero sense to me. In hindsight after this event, the iMac Pro seems like is was made as a stop gap until they were ready with their Pro level Apple silicon Macs. Perhaps what he might mean is that there is still a larger iMac in the works. I could see a scenario where when Apple refreshes the iMac with M2, they add a 27" option. Seems like that would be an easy way to increase the average selling price of the iMac. Maybe even offer an M2 Pro chip as an option in the larger iMac, I don't know. Regardless, a forthcoming iMac Pro seems extremely unlikely to me.
My prediction is that we'll see a preview of the Apple silicon Mac Pro at WWDC similar to the 2019 redesign announcement with availability starting in the fall. September will bring the usual new iPhones with a 4nm A16. Then October/November we'll see the first M2 chip Macs. Probably the Mac Mini, 13" Macbook Pro (if they're still keeping it around), and the redesigned Air. Then next spring see the M2 iMac. M2 Macbook Pros in summer/fall of 2023. Etc.