x mount FF
As I understand senors (basic), if I were to take that x1 pro sensor multiple it 2.25x (scale it to FF), I would see benefits in IQ because of greater resolution (36 MP), better ISO performance, and I believe better DR with more surface area (photosites). I would really love though, if fuji release a 24-28 MP full frame, not a 36MP like Nikon. 24-28 is plenty. Then they can focus on other areas of IQ.
More than any other camera maker, I am excited for Fuji. They really seem to understand the serious photography crowed---released a retro camera, mirrorless, wonderful sensors. No AA filter. Superb color. Prime lenses. Small package with great build quality. What a package. Only company on the market seeming to "get it."
I have lost faith in Sony. Both in a-mount and nex (horrible lenses). Canon keeps trying to make everyone videographers, and they seems stuck in 2007. Nikon is doing well, but more expensive and stuck in the same old, same old.
But the X1 pro's IQ seems good enough to me, so my real concerns are depth of field and my lenses not being the "right" lengths. I now shoot a sony a850, and if you switched my lenses (such as a my 24-70 to 36-105) it instantly becomes far less useful. I would love the Fuji at 18mm and 35mm. Not as impressive with cropped field of views at 28 and 50. And I really do like having more control of my DOF. I might not always shoot at 1.4 or or 1.8, but like many things, you pay just for the flexibility and ability to use thin DOF.
It's funny. Somewhat like the x100 (to me), this camera has me wide eyed--but not grabbing for my wallet--yet. We will see, but it seems Fuji has some of the best, if not the best, sensors tech on the market, a great heritage, they listen to their customers, truly understand serious photographers, aren't try to jam video or excessive resolution, make wondrous lenses. And yet they don't hop in full frame segment.
I feel like this is their m8, and a m9 will come. Hopefully soon.