My 2 cent considerations:
IMO the possible release of a MF mirrorless camera could be a smart move by Fuji. Instead of competing directly with the Sony A7 mirrorless system in 36x24mm size size, they would accompany their more compact APS-C size X mirrorless system by a larger one covering user applications that require the highest image quality. Such mirrorless cameras were rather popular and successful in 645, 67 and 69 size during film times (with and without interchangeable lenses by Fuji, Mamiya and others) and they already showed the weight and size advantage of mirrorless systems compared to mirror-reflex systems. The today's technology advantage is, that such a camera must not be nessesarily a rangefinder but due to the digital sensor one can frame and focus perfectly using the latest excellent generation of electronical viewfinders.
Fuji already works with Sony sensors in their X series cameras so it's rather probable that they would choose the 44x33mm 50 MP Sony sensor for their cam which is great because this sensor provides the currently best combination of "resolution times dynamic range" plus required life view capability (via EVF or back screen). My hope is they would make the cam with interchangeable lenses (not fixed like X100) and with EVF (not rangefinder - EVF combi like X-Pro). Basically a scaled-up X-T1 with all these nice manual dials, so you seldomly have to scroll through the menus. Regarding the lenses my recommendation would be my preferred 4-lens-set-up (others might disagree :-) covering the 21-35-50-85 mm range in 135 format. The speed should be a good compromise between speed and weight/compactness, so my favorites would be (135 equivalents in brackets):
25f4.8 (= 21f4)
43f3.4 (= 35f2.
65f2.4 or 2 (= 55f2 or 1.7)
105f2.8 or 2.4 (= 85f2.4 or 2)
That would make a still compact and not too heavy system (compared to a mirror-reflex sytem like Leica S, Pentax 645, Contax 645, Phase, Hasselbald H), maybe not larger or heavier than a 5D, with a really top notch image quality. And the price for the body would be a fraction of a Leica S or a Phase + IQ250/Credo50.
The really cool thing is that such a camera - additionally - would offer a lot of the capabilities of a FPS + IQ250/Credo50 system (again for a fraction of the price): The short flange distance of presumingly about 30mm would allow many kinds of mechanical or electromechanical adapters and shift adapters to mount MF lenses of any kind for architecture photography. And even a Canon EF to Fuji adapter can be considered because between the two mounts is enough space (about 15mm) and therefore the Canon 11-24, TSE 17, TSE 24, 85f1.2 a.s.o. could be mounted or the Zeiss ZE 135f2 Apo, Leica R 180f3.4 Apo, Leica R 180f2.8 Apo ... which all have sufficient image circle for the 44x33mm sensor. Such an adapter (by Metabones or others) could provide auto aperture and even autofocus with Canon AF lenses.
So: Fuji please go ahead and just do it :-)
Christoph