Thing about digital MF is it's no where near the size of most film MF, it's more like FF on steroids. I think the S2's sensor is 30x45mm, Hassleblads 33x44. In medium format film the smallest was 45x60, and laterly the most common 60x70.
There is a subtle difference when the light image falling on the sensor ( or film) is larger. In some (many) styles of pictures there is no perceivable difference, but in others it is there.
The recorded image on digital MF is nothing like as large as film MFs, and with the rapid gain in digital technology the benefit to many of using MF must be diminishing. Certainly nearly all the pros I knew who used MF film all use FF now There is one I can think of who uses Hassleblad digital.
The introduction of really good FF big megapixel cameras can only keep reducing the sales of MF - IMO.
So can't see companies like Canon or Nikon ever considering it !
I need to correct your post:
(the big) hasselblad sensor size is 40x54mm
same size like the phase one backs.
yes, the MF-film was 60mm tall but only 54mm are/were used !!
so effectively the big hasselblad and phase one sensors are exactly the
same size as the good old 645 MF systems.
and the difference between MF and FF is not only the size of the sensor.
CCD, better lenses, 16bit, fast flashsyncro /leaf shutter up to /800, ...
so there will remain a gap when canon introduces their big megapixel body.