What is certain for me, after owning, P45+, IQ160, IQ260, 3100, the IQ4 has amazing image quality. I see it each time I use the camera. With Frame averaging, (not used by me as much due to subject motion) and Dual Exposure, I am always amazed by the results of the images. Dual exposure to me for the way I shoot and subjects, has to be the single greatest feature Phase ever came out with. Namely, it works, and the results are just totally impressive. Not only do I see cleaner shadows and no longer have to consider a bracket for sunrise/sunset scenes, or other harshly lit scenes, the images seem to have even more sharpness in the areas where Dual exposure is giving the advantage, (shadows). It's so easy to do a quick comparison of a ISO 50 shot and a dual exposure ISO50 shot, and see the differences.
2020 has not been a good year for me or by business, but I do hold hope that the situation in the US gets somewhat better by the 2nd half of the year as I will be able to venture out again. I have a long list of spots in my local state that I wan to revisit and use the IQ4.
I have only one limiting issue with the Phase system, be it on Tech camera or XF, and that is for me it always requires a tripod, as hand holding the system just won't work, with wides or especially a long lens.
The GFX100 allows for much for shooting versatility and I can easily hand hold even the 250mm with the TC 1.4 attached. Unlike trying to hand hold the XF and 240mm. But the image quality IMO between the two systems is vastly different. I don't see the same DR with the GFX100, and almost always end up using a exposure bracket (which is easy to do and can be done hand held). but that requires more work in the post. The ability to just take one image with the IQ4 and dual exposure is really a huge advantage.
Phase One and the IQ4 only has really one raw converter, Capture One, as Adobe has never really spent anytime working on the raw conversion and it's less than stellar, and can't handle the dual exposure images, and this is not any different than the Adobe conversion for the 3100, which always had terrible red cast in areas of shadows.
The GFX100 files work with either LR/ACR or C1, but I sure wish Fuji would look at some of the results from the Phase One IQ4, either Frame Averaging or dual exposure and make a similar update to the GFX100 as in theory, there should be no reason the GFX100 can't do this as it has the same chip as the IQ4, just smaller. It might be a limitation to the processor on the GFX100, and or the abilities the Linux OS gave Phase One. The 400MP pixel shift solution that was finally brought to market, IMO is a total waste of time. Can't be used outdoors at all, unless you are in a area like Monument Valley, or the Grand Canyon, and even there I believe simple wind might cause enough camera shake to ruin a series of images. Unlike Olympus system which processed it's output in camera, Fuji relies on a external software package, that is less than stellar also. The files are not stored in a separate folder on the card, and it's difficult at best to keep up with them if you have shot a lot of other images mixed in. As it took Fuji 1 1/2 years to get this feature out, and this is the best they have, I don't see it changing much. So to Fuji, my take is figure out a dual exposure, or frame averaging solution. Single files even at base ISO in my use don't have the same degree of DR push.
Phase One's single biggest issue for me is just total lack of information, both on current features and up and coming features. Look for example to the "highly" vaunted EXIR feature that was given so much press with the launch of Feature update 8. Net, "it works with any IQ4", which is total BS, as it currently only works with the XT (go figure) and was not even tested to work on the XF, even though feature update 8 supposedly added so much new stuff to the XF. This is just one example. Another would be why can't you kick off frame averaging with the Bob or other remote release? Simple stuff, should have simple solutions. Instead Phase has been totally seemingly focused on the XT platform. The single most expensive tech camera ever released, with NO easy upgrade path of owners of other cameras. Folks, it's just hard to justify 13K to 15K for a lens (32 HR-W with XT shutter) and 7K for the XT. With no trade in path it's cost prohibitive to consider such a solution. And if you think that shipping off a existing tech camera lens to have the shutter changed is worth it, I would consider this, way too many hands will be handling the lens, and the odds of getting your lens back with the same exact degree of sharpness or focus to me is a huge gamble. These lenses alone are just to fragile. The only way to really assure such is to purchase a new lens, tested from both Rodenstock and your dealer to work on the XT, which is a huge cost.
Enough, I rambled. Just wanted to point out that Phase One did score some amazing points with features that have been added to the IQ4. Hopefully 2021 will see further improvements.
Paul C