I am a wedding photographer who has done some work with small businesses and is trying to get editorial stuff too for smaller publications so, I've been thinking about the GFX a lot. As a camera, I like a lot of what I'm seeing. I loved the 645z when I'd rent it, and Fujifilm has brought that sensor a better, more rounded system. That's super cool. This seems way more targeted at every-day pros than the X1D (no knocking that beauty, just saying).
OTOH...
I have a hard time convincing myself that I need to spend $8k for one camera and 1 lens. Yes, my absolute IQ will go up, probably a lot. But the 63/2.8 is really like dealing with a 50/1.8 in 35mm terms. On my Nikon I have a 58/1.4 which is like a Noctilux for DoF, and a ART 50/1.4 which is a pretty insane amount of sharpness. All of my other primes are 1.4. The sensors in my two bodies are pretty dang great. Low to high ISO, no complaints, with a ton of room for cropping. The AF is essentially state of the art. I'm just not sure what I'd be gaining with the GFX. I really like that it exists! I think it's super cool. But I'm not sure it can do all that much that a D810 can't already do. I'm more coming at it from a pro, ROI, perspective of course. I'm not even arguing that it should be cheaper, I'm just saying it seems harder to justify 33x44 these days. I mean let's be honest...
D810
D750
Sigma ART
50/1.4
35/1.4
24/1.4
85/1.4
=$8000.00
Or:
GFX + 63/2.8
=$8000.00
Now different photographers have different needs but as a wedding shooter...I can see what makes more sense at least on paper to me. Maybe down the line if my business is just swimming in cash and I need a tax write off I could see getting into it. Right now though...even that aging 36mp sensor is more than I often need.