Hi,
I don't think it is an either or situation. I would recall that Jim Kasson calculated that contrast extinction appears at 2.9 micron pixels for f/11. So, what happens when we stop down beyond optimum is that we need to sharpen more. Sharpening may cause artifacts, though.
I would think it may be reasonable to choose resolution according to print size. Say that I would print at maximum 30"x40" and that I would need 180 PPI for an excellent print. So, I would need 39 million good pixels. In my case I have a 39 MP Phase One P45+ and a 42 MP Sony A7rII. Both would just fill the bill. But, rendition may be a bit coarse and it may need pretty aggressive sharpening to get there. Having more pixels may result in a smoother image, needing less aggressive sharpening.
Shooting in DoF limited settings, there would obviously be a balance, stopping down reduces the blur caused by defocusing but increases the blur because diffraction. Optimum is probably when CoC from defocus equals the full width half maximum of the diffraction blur, or something like that.
Nothing of this is new, it was well known in the eighties. But in that time we needed a microscope to see full detail in slides. Just to say, I had the opportunity to check out slides on a professional microscope at 100-400X magnification and that was an interesting experience. Now days we can just open an image in Lightroom and zoom to 1:1 view.
Best regards
Erik
That limit to largish apertures and lowish DOF is an inherent trade-off for getting “100MP worth of detail”, regardless of camera model or format size. Yes, at 100MP and up, such trade-offs do significantly limit use cases, at least for single-shot photography (no focus stacking). The good news is than when it is better to stop down for more DOF, the sharpness is never less than with a lower resolution sensor; it is just that the resolution gain from the higher MP sensor is partially lost to diffraction.
I’m guessing that by 150 to 200MP, the extra res. will mostly be achieved with almost flat or very distant subjects: paintings, aerial mapping/surveillance and so on. Or very stationary subjects, allowing focus stacking.