You are unlikely to get the full performance from Alder Lake in an iMac form factor anyways, given the high power draw and heat generated. As it stands, Alder Lake only makes sense in a desktop configuration with lots of room for heat dissipation, and only the Mac Pro currently offers that (and Apple uses Xeon chips for that).Don't understand why Apple won't offer the Intel Alder Lake at least as an option for those who need a no compromise machine. Bypassing it for the slower M1 guarantees that iMac Pros won't be very Pro.
My guess is some time early next year, Apple stacks 2-4 M1 Pro / Max chips together in the iMac and benchmarks beat Alder Lake, and you still get the benefit of sustained performance in a cool and quiet environment no less.