Remember a couple of things here that CAN affect RAM usage potentially:
1) Apple Silicon cores are FAR different than other ARM. They are WIDE (8 wide no less), have a ton of fast cache and a huge number of execution units among other things. This means it can send a lot more stuff to the CPU where it is not sitting in RAM and can also hold more in cache again not needing the RAM.
2) Apple Silicon has a bunch of coprocessor blocks that take load off the main GPU and CPU. Again this means things are not sitting in RAM as often or as long.
Long and short - the only way WE have to see how much RAM is actually needed is real world usage. Apple may know but we do not have that info.
Neither of these impact RAM usage in the way you are thinking.
Caches hold
copies of data. CPU caches hold
copies of data in RAM. RAM caches hold
copies of data on disk. CPU cache size has zero effect on RAM usage, and everything to do with not starving out that execution pipeline. Those coprocessor blocks use RAM caches (buffers) to hold the input and output of the work being done. Software manages those RAM buffers, writing to disk and loading fresh data. But this is how it’s been done for ages. Nothing here has changed, just because say, Apple’s HEVC encoder block is faster than Intel’s. If anything, it’s more likely these buffers would benefit from getting bigger, not smaller.
I completely expect RAM usage on the M1 to be similar to Intel. They still use the same concepts when it comes to memory management that have been in use for decades. x86-64 and AArch64 have similar memory alignment requirements for efficient load/stores. There’s not enough changing here to impact things. Not big enough to change someone’s decision on how much RAM to buy for their system at least.
I’ve worked on projects where we used the same code on iOS and macOS, and we never really saw a difference in memory usage between the two for the same code. At least not when comparing x86-64 and AArch64. The bigger differences were driven by the fact that iOS would warn apps about memory pressure and cause us to free internal buffers more aggressively. macOS just pushes stuff to the swap file under memory pressure instead.