I'm not familiar with the cr8 or cr10 hot end mount, I'll take a look and see if I can make that work. There is a quick change picatinny rail mount variant of this in the works as well, I just haven't finished it. Same thing with the dual extruder. The rotation on movement is definitly a concern, so far in testing where I have the motor mounted is close enough to inline with the travel axis that it doesn't seem to move enough to cause a noticible variation in the part with the high gear ratio. I'll see if I can't incorporate a moving mount of some sort. My concern is that allowing the motor to move would actually decrease accuracy on start of shaft movement because the motor might turn instead of the shaft. ( kind of like the old cartoon where the guy holds the airplane propeller still and the airplane body spins instead.) The overall mass difference would probably prevent that but it's something I'll need to account for if I go that route. Thank you for your interest in the project and your feedback!