I don't think photographers using H series cameras for a living are likely to use an X1D of GXF with their H lenses. They lose AF and, in a commercial settings, that is probably not an option. Just as well: I don't think the very limited selection of lenses for these cameras makes the X1D or GFX a viable alternative for most professional users. I believe that the market for mirrorless MF is mainly rich amateurs.
Then, the professional photographers I know to use medium format cameras use them in a studio setting for the tethering function. One needs the central shutter high-speed flash sync. The others mostly do product photography and do not need a high pixel count, so they did not upgrade from the H4 or even more ancient models. They will be compelled to upgrade when firewire dies on them, but not before.
The rental market also appears to have changed in the past two years. It used to be that one could rent medium format cameras and the full selection of lenses in every large city in Europe. I may be mistaken, but the offer appears to have shrunk considerably (only for medium format, not for lights, etc...). You can rent the X1D or GFX, but mainly from rentals catering to advanced amateurs. Using the rental market as a proxy, I therefore believe that medium format has lost market share for the kind of production where a pro is likely to rent (not the one doing product shoots all day in a studio, it makes business sense for these to buy or lease). I think this was to be expected, since 24x36 has become sufficient for the majority of this kind of shootings (except, maybe, when flash is needed outside).