Fuji has made plenty of rangefinder 6x7 and 6x9 lenses in the past (which were also very compact), this will be nothing new to them.
I guess a good starting range, considering the crop of the 50MP Sony sensor, would be 45mm f2.8, 65mm f2 and 110mm f2.8 (equivalent to 35, 50 and 85).
The big question would be: lens or focal plane shutter? The first would make the system quite interesting for studio work.