I think the question posed by AeroPhotographer is a good one and it's worth keeping in mind. My post is going to be a tangent from it, so I hope it isn't a nuisance, and anyone is welcome to skip over this long post!
I am not yet a medium-format owner though I hope to become one. And my reasons for wishing to have nothing to do with resolution. Indeed, I think resolution has become spuriously high, and it will only get sillier if it is taken further, but that's just me.
What interests me about the Fuji medium format offering does relate to what it will do for image quality, for me, in the end... but it has nothing to do with resolution.
I like to take posed telephoto portraits. It seems to just be my thing. I like the look created for people-photography by a big long lens.
Often, it can produce a pleasing perspective to take a long-portrait shot from a low angle.
When I do this with most cameras, I run into problems. On almost every camera the viewfinder is fixed and horizontal, and so I cannot use it, either at all, or without contorting myself painfully (which then means that I do not shoot much, or for very long, before giving up), when the camera is down low in a good position for that perspective I am seeking.
The rear LCDs on my own current, not-latest-gen Sony full frame cameras do not tilt in a way that is a help when shooting in portrait orientation. In landscape orientation- sure. But not portrait. And, even if they did tilt in more axes (like the newest Sony bodies)... it'd be welcome, fine, but nevertheless, a rear LCD screen does not always work: On a bright day, the LCD, tilted, is competing with glare from a bright sky and I find it is sometimes unusable. I can force the LCD screen to overboost its brightness, in what Sony's menus call "Sunny Weather" mode, but then I can no longer judge whether the image is correctly, over-, or under-exposed because the contrast and brightness has been so forced. I find that in Sunny Weather mode, unlike in normal LCD brightness modes or when using a viewfinder, I often misjudge and apply heavy Exposure Compensation at the time of shooting that is far wide of the mark and leaves me having to push the RAW file hard in post to make up for my mistakes, which, despite best efforts, compromises the resulting image.
Some Fuji GFX cameras, almost uniquely, have both a highly flexible tilting LCD and a good, adjustable, tilting viewfinder. Problem solved.
Further... I like to shoot with long lenses, as mentioned. Such as the Canon 200mm f/1.8 and 400mm f/2.8. I like the character and look of these lenses and there aren't many alternatives or substitutes to what they create. With such lenses, of course, framing is often tight(!). But they have wide image circles, which can illuminate more than a full frame sensor and can work, adapted, on a GFX sensor. Use of these lenses with a GFX camera would change their working distances just a tad, in just the ways I would find very helpful. I've noticed that I have a hard-coded tendency to be almost, but not quite, far enough from my subject when I first judge my position and distance. I find the image is framed just slightly too tight at my first guess, time and again. So I have to get up and move position again. I seem to keep doing this, even as I keep it in mind. Which adds to the faff and delay in getting the portrait shot - which, potentially, affects what image, or how many images, I end up getting, depending on the situation and the patience of my photographic subject. So the tiny dab of extra frame-space added by the GFX framing on these lenses would fit me like a glove.
Even if I do not find myself slightly too close to the subject on the long axis... especially the short axis of the image, in portrait orientation, is often too tight. I really covet the 4:3 aspect ratio of the Fuji GFX system, as on 3:2 I find the framing very unforgivingly narrow, and the edges of the frame claustrophobic for portraits even when no errors are made at the time of shooting.
Putting it all together: I often can't quite see what I'm shooting in daylight, my framing is ever so slightly too tight anyway, and as I'm half-blind with VF and LCD limitations some of my shots get thrown away because I haven't realised I'm a tiny but decisive fraction aimed too far left or right and the narrow 3:2 ratio leaves no room for error or an unbalanced framing (you can't crop it back to balance). I take longer to get the shot, I'm more clumsy, hesitant and underconfident doing it, fewer of them work, some are badly over- or under-exposed.
The net result is that a GFX camera would give me a more correctly-exposed image, a better-framed image, a lower-stress and lower-pain shooting experience with less dithering and delay in framing up the shot. All of that will, I believe, improve my shooting in a "perceptible" way - the contents of the resulting image will be better, for all these gains. None of it is resolution. I want a GFX!
I just have to keep saving for one that has decent people-autofocus (to not lose all my other gains in time and convenience by a different avenue) which, unfortunately, won't be cheap.
I really do feel that resolution, as currently offered, is already spuriously high. People often point out that the original GFX50S sensor is no longer manufactured, and fine, good riddance - it was an odd sensor... with no PDAF, with its overly-squinty, moire-inducing microlenses, its old-fashioned lack of BSI light-gathering capability, and its slow readout (all of which I could forgive, perhaps, except autofocus, and additional moire induced on people's outfits)
The sensor used in the GFX100 models is essentially just a larger version of what Sony puts in its A7Riv and A7RV. Same pixel pitch, just bigger. Why not do the same, with the sensor Sony puts in the A7iv? (non-R). With that sensor's pixel pitch, you'd have a modern, good 55 megapixel BSI GFX sensor with all the resolution, capability and flexibility I could want.
I appreciate that my needs are very niche and that the above suggestion will never happen. High resolution is the easy quotable selling-point of the GFX system that they are unlikely to compromise on. I'll end up having to buy a GFX-one-squillion model, eventually, when I've saved up enough. I'm just emphasising - I don't need the resolution, but I do seek a perceptible image quality result difference from Fuji GFX. I hope this post didn't derail/detract too badly from the original poster's question, but I feel that maybe the quality-of-life upgrades, and what they do for the final image, might be worth mentioning with my one niche example.
