I agree with some of OP’s points and disagree with others.
I think the desktop lineup will look something like:
iMac Pro - M1 Pro, M1 Max, M1 Max Duo
Mac mini (high-end) - M1 Pro, M1 Max
Mac Pro - M1 Max Duo, M1 Max Quad
Mac mini and Mac Pro will not overlap at M1 Max in my opinion. The Mac mini should be able to accomodate it, and including it in the Mac Pro would require a severe reduction in start price (an M1 Max iMac Pro would probably be mid to high $2000s, so an M1 Max box with no 5K display included would need to undercut that).
Disagree that the Apple Silicon Mac Pro will offer expandable RAM. As another commenter mentioned, we have seen evidence of a refresh of the Intel Mac Pro, which would only make sense if it is set to co-exist with the Apple Silicon Mac Pro for some time. I think the significantly higher memory capacity is one of the key motivations for maintaining it. We’ve also heard that the AS Mac Pro is a much smaller chassis, which would imply more limited expandability.
My guess on the timeline is that the iMac Pro and Mac Pro will be announced with M1 generation chips in Mar/Apr and June (WWDC) respectively. The first M2 MacBook will then follow in the Sep/Oct timeframe. I think there is a very real possibility that M2 skips a generation to be based on A16 (note that M1 came out very quickly after A14, and CPU gain from A14 to A15 was minor), with M2 Pro/Max/etc following by mid 2023. I think Apple could then switch to a one year cadence from then on, as they will no longer be contending with the semiconductor shortage and the challenges of ramping up new larger chips for the first time.
Somewhat related to this thread is a thread I started re. the BTO options Apple would offer for dual and quad M1 Max configurations if anyone is interested:
https://forums.macrumors.com/threads/possible-mac-pro-chip-options.2318399/