I was going to post this as an answer to another thread, but the I figured it might be worthwhile on its own. I've had possession of my X1D for all of five days now so I'm still at the early stages of understanding the capabilities of this camera and its operation. I've shot with it on the streets of NYC, the beachfront in San Diego and for a variety of environmental portraits along the way.
Before deciding on the X1D, I looked at the GFX in the store. I picked it up and then put it down never to consider it again. First, the low sync speed is a real issue for me. I regularly use strobes to overpower sunlight so I need the higher sync speed. Second, to the eye and to the hand, the Hasselblad is a Ferrari and the Fuji is a Ford Pinto. While I'll grant you aesthetics are on their own no reason to drop a stack of cash on a camera, if you are going to spend the money, better to spend it on something that just looks and feels amazing - which the X1D is and does.
The X1D is the most elegantly designed camera I've ever held in my 27 years of professional experience. It feels great in the hand. You just want to pick it up and shoot with it. More than that though its compact and sleek size makes it a capable daily shooter. My H5 generally stays in my bag unless I'm doing a setup shot where weight isn't an issue. (I've tried doing environmental projects with it, but you've really got to want it and be prepared to make some sacrifices.) The X1D can do double duty: it will handle the pro work and the street shooting. Put a camera strap on it and head out the door. In looking at the GFX, while I'm sure you can use it like you might a smaller format camera, its boxy, oversized shape makes it unlikely that you'll want to.
I weighed my Fuji XT2 with an 18mm lens, Nikon D810 with 28mm f1.8 and the X1D with 45mm lens. The Fuji was a full pound lighter than both of the other two. The X1D weighed in two ounces less than the Nikon! (Two pounds, eight ounces for the X1D.) For the most part, the X1D acts less like a traditional MF camera and more like a small format camera, albeit a slower one. The AF is much faster than the H series though slow by DSLR standards. 6400 ISO is highly usable. A 6400 ISO test print at 11x14 looked great. The soft clicking of the leaf shutter is both quiet and doesn't sound like a traditional shutter - a big plus for working unobtrusively.
For my walking around images, I found myself using the Aperture priority mode - which was generally spot on even in backlit situations. I haven't dug too deeply into the files themselves. Overall, they look like what I expect - sharp, good color, plenty of highlight and shadow detail.
In the things-I-don't-like category, I'm having an issue with the shutter release that needs to be resolved. Also, when shooting with polarized sunglasses, the viewfinder is completely unviewable in landscape orientation (works fine when leaned over to vertical). There's some odds and ends bugginess as well that I hope will be cleaned up in future firmware upgrades. The camera itself takes some effort to learn and adapt to its ways. The viewfinder blackout took me back at first, but now I'm used to it and it doesn't unduly slow me down. A thorough reading of the user manual is essential.
What I love about the X1D is that for the first time, I can truly embrace medium format as a viable format for my daily photographic needs. I can use it for my studio work, street work, landscapes, and even tourist snaps (if I'm so inclined). It will become my primary camera. If I need more speed and even less weight, I can turn to my Fuji XT2. The loser in all of this is my Nikon because it's in the middle getting squeezed. The day may soon come when I sell it off and stick with mirrorless formats.
The final question to be answered is: Will the X1D offer results that you can't get with cameras costing a fraction of the price? Excepting for possibilities offered by high sync speeds working with a flash (which for me is big), I'll say no. Though I shot with MF film cameras and have owned the Hasselblad H series now for almost 10 years, I don't subscribe to the whole MF "look" thing. I just don't see much difference between formats in the final images anymore. If you've got the money, the X1D is a great camera just like a Ferrari is a great car. If you don't have one though, don't worry, you'll still get to where you're going.