The Fujifilm GFX50R is now marked as discontinued at BHphoto here.
There is still a massive deal running on it, but the camera gets harder and harder to find. Still some samples are available at Adorama here.
I don’t know when/if Fujifilm plans a successor. But if they do not plan one, then this would be a massive mistake. the GFX-R line has a small but very loyal fellowship.