I wonder how many MP-E 65 users actually use it primarily in the field? I don't think it was really designed as a field lens, it really is far more at home clamped to a serious tripod at home. Once you get down to 5x you're pretty much required to stick to f/2.8 because of diffraction which means your depth of field almost doesn't exist, so unless you're shooting perfectly flat things you absolutely need to stack, and that's no fun out in the field
I think you would be surprised. While the MP-E is great on a tripod, it’s an excellent field lens if you have some practice with it. With the MT-24EX/MT-26RT it’s one of the most convenient solutions I’ve ever used since the flash heads move with the front of the lens.
While it is a good lens at 5x, I would say that there are much more capable microscope objectives that also cost less. Yes, you lose aperture control, but again diffraction is such an issue you didn’t have it to begin with really. I’ve found that Nikon objectives are reasonably priced, very sharp, and relatively distortion-free. Not saying that the MP-E can’t be used for this, but I think microscope objectives provide a much better result. I’ve stacked quite a few times with both, and much prefer the microscope objectives.
Attached is my microscopy rig, of course without lighting and subject. I use a specimen manipulator to move the subject as opposed to the camera. I’ve also attached one of my best results with it.
This all being said, and trying to stay on topic, this patent definitely isn’t for the MP-E’s successor. It is probably a workhorse lens that Canon could also sell to the masses as a good portrait lens as well. From my original comment, it’s just wishful thinking