I envision both MacBook sizes will use the same set of SoCs for economy of scale, maybe an 'M1Z' (see below) will be exclusive to the 16" similar to how dedicated graphics currently are, depending on how much heat it produces/ what the thermal envelope of the 14" is. I think your M1X core counts might be slightly optimistic at this stage.
M1X options with a 12(?) core GPU, probably a 30-35 watt TDP:
M1X - 10 cores (6 firestorm, 4 ice storm) - corresponding to the 6 core i7
M1X - 12 cores (8 firestorm, 4 ice storm) - corresponding to the 8 core i9
And at least one M1Z option with an upgraded 24(?) core GPU and likely a higher TDP to facilitate that:
M1Z - 12 cores (8 firestorm, 4 ice storm) - upgraded graphics option
They've already established with the iPads that 'Z' processors are graphics enhanced versions of 'X' processors, so the logic is in place for this already. I don't think they will simplify the upgrade tree too much, plenty of extra options are a good way of getting people to dig deeper in their pockets and raise average selling prices (which is an important metric in their financial reports). Assuming those three chip options each have 16, 32, 64 GB RAM options, that's 9 chip SKUs, for two MacBook Pros and likely a high-end Mac mini. They could trim it a bit by making 64GB exclusive to the M1Z.