If I were to guess, I would say that Apple will follow a similar model to the MBA where cores are enabled/disabled.
Not only does this make it easier for them to manufacture a small range of chips, but they can also use 'binned' components for the disabled chip models, and just focus on a generation per year rather than incremental performance changes.
Keep in mind that even with the upgrades on Intel models, the performance improvements are often negligible. We've recently seen scores that are anywhere between 5-15% better, but at a considerable cost - over several hundred dollars. And that's with thermal throttling, too.
And since the M1 is already such an impressive chip, I believe Apple will continue with their annual cycle and keep tandem with the A-series chips.
My predictions for the M-series (Where '1' refers to the generation at the time of release) are:
MBA, MBP 13", Mac mini - M1 (lower-end)
MBP 16", iMac - M1X (mid)
Mac Pro - M1Z (High-end)
I also believe that the lower-end models will continue to have integrated graphics, whilst the mid range and above will have dedicated graphics options from Apple - again, with cores being the differentiator. As for the Mac Pro, I can see a range of MPX modules just like the Afterburner card being produced by Apple, which would also allow for the case to be condensed as per the rumour.