Well, while having the memory in the packaging has brought the M1 great memory performance for their workload (the IGP is even more impressive than the CPU) Apple being Apple you have to wonder if putting it in their with zero ability to upgrade was solely for technical reasons.
Sure, a hierarchy of memory would be harder to manage but someone wanted to I see no reason why the 8GB onboard could not be supplemented by a SoDIMM or two.
Or even if the hierarchy was supplemented with some NVMe SSDs / Optane etc. to use as super fast swap (although swap and wearing out the build-in SSD is probably a sore point for anyone who has bought a M1 device - another brilliant bit of planned obsolescence by Apple as the SSD is soldered on too
AFAIK).
Everyone watches Apple, so I expect more of that kind of throw-away consumer junk with planned obsolescence. All the more pity that ARM / Qualcomm etc. are nowhere near the M1 in terms of CPU performance.