No one, not Hasselblad, not Phase One, not Sinar or Leaf has access to a sensor larger than what is currently available from the two main sensor manufacturers: Kodak and Dalsa. So constantly harping on the digital back companies is a waste of time and energy. It will happen when Kodak or Dalsa make it happen.
50 meg will have its applications for some sectors of commercial photography, not just for testing lenses. Reduced moire especially for clothing catalog work, more minute capture of industrial product detail, scientific applications, archival recording, and to further enable the various multi-tasking size/cropping applications used by advertisers today.
ISO 800 is a novelty for most users of Medium Format digital backs. The native ISO 50 or 100 is the most used sensor speed in commercial studio photography using powerful studio lighting ... which in turn is the most frequent application of high meg equipment ... not shooting landscapes, frolicking pets or flowers in the backyard. For more energetic applications such as fashion and some high-end event work, ISOs are available up to 1600.
I am also of the opinion that the Fuji made lenses are optimized for specific types of critical commercial digital applications, and in most cases really do outperform their Zeiss counterparts in the commercial studio. This does not negate the fact that the Zeiss pictorial characteristics are highly desirable in certain shooting situations ... fortunately, we can use them on the H cameras with film (H1, H2, H3, H2F) or digital capture (all H cameras) via the CF Adapter.