So if A16 CPUs manufactured on the same process as the A15 might be cheaper to make en masse because of the higher yield? I think there's an argument to keep the lower end machines as cheap as possible.
Correct. N5P yields are well over 90% so the "waste" is likely quite low and why Apple can sell almost all of their M1s and A15s because the ones that do have defects have very few (the "binned" models). Building A16 (and, perhaps, M2) on this process would also mean most of the SoCs would be usable.
This might explain the high end camera modules we've seen for the iPhone 14 Pro but what can Apple offer in for Macs using the high end CPUs to help offer better value?
As you (and others) have noted, in the end, M2 is just a marketing name. And for some time M2 was thought to be using the A15's CPU and GPU cores, with speculation that it might be on A16's cores only really starting to gain traction as we grew closer to the A16's launch.
And let us not forget there were rumors M2 was entering validation production this time last year (around the same time A15 did).
Presumably this cost is silently carried over in the Mac Pro as that's not been released yet but where does it leave the Mac Studio and the 14 and 16 inch Pro laptops when M3 rolls around?
At the end of 2021, media speculation was that we'd see M2 likely in the Spring and the "professional" M2 SoCs in the Fall of 2022. I believe that roadmap, if it was ever official, is now out the window due to supply chain and manufacturing issues. Apple can't even meet demand for the M1 family, much less shipping millions of consumer M2 and professional M2 models.
I do expect M2 to launch either at WWDC or at a special Mac event in the Fall and we should see M2 refreshes of the MacBook Air, Mac mini and 24" iMac. Apple might also slip in an M1 Pro Mac mini at the same event.
As for M2 Pro / M2 Max / M2 Ultra, they might happen in Spring 2023 or WWDC 2023. Or Apple might end up just scrapping them and going straight to M3 / Pro / Max / Ultra at WWDC 2024 with everything at 3nm.
Could we be seeing M1 and M2 pooling on the low end Macs for some time to come?
I think Apple will continue to offer the MacBook Air and Mac mini, at least, on M1 for the foreseeable future to lower the minimum entry price to try and pick up some more budget-conscious customers. Same with the M2 models once M3 becomes the normal.