I stopped by CI back at the end of May and met up with Steve and a representative from Mamiya so I could get my hands on the Leaf Credo 80, and compare it against the Aptus 12. My impressions are that everything about the Credo screams quality, speed, and accuracy. I had the same qualms about whether or not the lack of rotating sensor would be a make it or break it feature, or the tilting screen, but... at the end of the shooting session, I was pretty well convinced that I would not be happy with an Afi-II 12 knowing how much better a shooting experience there is with the Credo.
For starters - the tilting screen on the Afi-II 12 is more necessary than one may realize at first. The LCD display quality drops off dramatically if you are not viewing it straight on, and so being able to tilt the screen to be parallel to your viewing angle is actually pretty important. With the Credo, this simply is not the case. The LCD remains very bright and detailed from much more of an off angle than the previous generation screen, to such a degree that you no longer need a tilting mechanism to overcome the off-angle drop off in quality.
The rotating sensor, to me at least, is overshadowed by the sheer speed of the Credo. Previews pop up within 1 - 2 seconds after taking the shot, and you can buffer a lot more shots than you can with the older Afi. Also, zooming in to 1:1 is very much a night and day experience - much faster, much snappier on the Credo. I can definitely see how being able to rotate the orientation of the sensor, especially on the Hy6 body, can be useful, but it's not a deal breaker to me. I could just snap on a 90 degree prism and rotate the body while holding the grip handheld, or do the same while on a tripod. My preference would be for the much more responsive workflow of the Credo back by comparison.
Now - shooting detail, I have to say, was very hard to see much difference. I can't remember the exact results, but there was some slight difference in comparing the images coming out of both backs, but nothing that couldn't be corrected in C1. Fully corrected, images from both backs appeared stunning (to my eyes anyway, coming from a meager Afi-7).
So... I am pretty well sold on the Credo, to the degree that I would even consider switching systems if it meant that Leaf decide not to ever implement an Hy6 mount. For now I am in a "wait and see" mode, since I do still shoot majority film vs digital with my Hy6, and have already committed to Steve that I'm ready to upgrade from my Afi-7 to a Credo 80 if it becomes available for the Hy6. If there are others who are interested in buying / upgrading into a Credo back in an Hy6 mount, now is the time to make your voice heard!