The next medium format camera from Fujifilm is expected to offer an even higher resolution than the expensive Phase One XF IQ4. According to the latest rumors from a reliable source, Fujifilm is currently developing a GFX camera with a 180MP medium format sensor.
As a real life example, the Canon 600mm F11 telephoto lens should be awful, on, say, a 32MP crop sensor R7. That’s insane pixel density somewhere in the ballpark of this Fuji.
…But look at real life shots of that exact combo, and they’re sharp as hell. Sharper than a Sigma at F6.3.
The diffraction limit is something to watch out for, but in reality, stuff like the lens imperfections, motion blur, atmospheric distortion and such are going to get you first. You don’t need to shoot at F4 on this thing to make use of the resolution, even if that is the ideal scenario.