Well, for me, since yesterday but i imagine for the larger world its been a bit longer than that.
We have two H3d11 39s in the studio for the last few days and the last thing i was told by the dealer was to make sure and not put the backs on the wrong cameras as they will be "out of calibration".
So correct me if i am wrong but you cant even put a hasselblad back on another hasselblad camera of the same model and generation without sending it to Hasselblad.
So i would have to deduct that putting it on anything else is not going to be a realistic option.
So the only advantage i can see of being able to take the back of a H3d or H4d i assume is to clean it.
And to put it in the context of this thread, if it's that hard to control the alignment of a back then i am now starting to view the integrated approach of the Pentax and S2 as an advantage.