I think Tim's comments are pretty much on the mark. Now if Fuji could just make FP100C in 4x5" and 8x10" sheet formats that would be ideal, at least for proofing.
I did try a couple of transfers with the FP100C once and got something, but it just wasn't as easy as with 669/59/809. With the demise of Polaroid, there's a bit more incentive to experiment with it. Maybe it would transfer better with more heat, for example.