With the price and specs released, Fuji has done a nice job trying to make as many potential users happy as possible. Those who would use this lens in-studio should be fine with the f5.6 because dof below that is so shallow it is easy to have one eye in focus and the other out when not intended. I've had that happen with my Hassie lenses. And for those who want to take it on a trip, it weighs less than a Canon 70-200 f2.8 and not a lot more than Fuji 50-140mm. And the price as released is excellent if the IQ is like Fuji's other lenses, particularly the 32-64 zoom.
I think many who want a faster lens might not have experience using a medium format lenses in this range. Faster lenses are larger and heavier and more costly. For much studio work you might be using them above f5.6 much of the time anyway, as I generally do. Keeping the front element to 67mm and internal zoom is a plus for taking the 100-200 on the road. Nice compromise.