Fuji really changed things in the MF market here. Before the GFX 100, there was the "traditional" MF market, dominated by Phase One, but also including Hasselblad H-series and the occasional Leaf (etc.) - body+back, massive entry costs, upgrade programs made ongoing costs somewhat more reasonable. There was also the newer market for integrated cameras, pioneered by Pentax, now dominated by Fuji, with the Hasselblad X being the third competitor.
The integrated cameras have always been MUCH cheaper - $5000-$10,000 instead of $20,000+ and often $40,000+ for a body+back setup. The challenge has been that all of them prior to the GFX100 (and ignoring earlier Pentaxes that used a CCD sensor) have used the same older Sony 50 MP CMOS sensor (from 2014). The old sensor is certainly a good performer, but it isn't quite up to more modern designs, and its lead over much newer 40+ MP FF sensors is questionable. It's essentially of the same generation as a D800 or A7r (original) sensor, and its extra size only goes so far against the generational improvements in smaller sensors.
The body+back cameras, due to their even larger sensor sizes, maintained a comfortable resolution lead over 24x36mm - the Sony CMOS sensor that showed up in "almost 645" backs was not only slightly newer than the ubiquitous 50 MP model, it was (is) also 100 MP. It's still not latest generation technology (early 2016 and not BSI), although it brute-forces a really excellent performance with size and pixel count - but it's meant a $40,000 camera until very recently.
The brand-new 100 MP "small MF" sensor in the GFX against the IQ3/Hasselblad 100 MP sensor will be a very interesting comparison. My suspicion (from previous cases where one Sony sensor is both a size smaller and a generation newer than another) is that it's very close? That's a tricky situation for Phase One, because even a used IQ3 100 is twice the price of the Fuji - and anything that leaves the Fuji comfortably behind (IQ4 150) is four or five times the price of the Fuji.
For most types of images, the Fuji is easier to use (modern AF, IBIS, etc.) There are certainly limited circumstances where the body+back design (or the back alone mounted on a technical camera) is an advantage. How many types of photography are there where the design is enough of an advantage to pay the premium?
