Well, at least with any body which is in an open system like any Phase One or Mamiya body.
I'm kind of fascinated by this open system thing. Yes the Mamiya takes other backs but I doubt seriously if it was Phase's main purpose to make a camera for other makers digital backs and since the Mamiya in it's many versions has been around a long time, I doubt if it would go over very well if they had closed the system.
But all of this seems to be kind of a mute point because I'm rarely anywhere I can't buy or rent an H-1/2 or a Contax and that includes the recent three cities I've just traveled to.
I didn't check but I wonder if renting a DF in LA, Chicago and Detroit is easy, though I should say again, I haven't checked, then again medium format cameras (not backs but cameras) seem to last a very long time before they are outdated.
In regards to Canon making a larger than 24x36 camera who knows, but I also would place a guess that regardless of the frame size the next big camera thing will be an EVIL viewfinder camera that can shoot stills and (excuse me because I know everyone here hates this word) VIDEO.
I know there are a lot of rumors out there, always has been since digital film has taken over, though I also know that a few of the rumors out there will happen and some probably shake up the high end camera world even more.
I do know the last portfolio we showed was on an i-pad and the interest in the motion imagery was equal or greater than the still imagery, so it stands to reason that EVIL is on the way.