The non-Pro/Max versions (e.g. M3) uses 128-bits, and arguably is the kind of notebook that mostly needs to be upgraded later since they commonly come with only 8GB of RAM.
Even the Pro versions (e.g. M3 Pro) use up-to 256-bits, that would be 2 x LPCAMM2 modules, that seem plausible.
For the M3 Max in the Macbook Pro, yes, 4 x LPCAMM2 would be impossible (probably). But I think you could have something like the Mac Studio have them, that is arguably also the kind of device that you probably want to increase memory in the future.
