An often unfortunate aspect of automatic movements, at least when coupled with a display back, is that the rotor tends to hide much of the movement at any given time. Some rotors are hollowed out quite a bit, and that helps, but I keep wondering why all the movements use a central axis for the rotor.
I've drawn a picture below to illustrate what I mean. I apologize for the crudeness of it, I'm not terribly good at image editing. Next to it is a picture of an annular gear.
There could be a large outer ring, with gearing on the inside, probably mounted a ball gearing attached to the outer circumference of the case. That could freely rotate around, which would wind up the movement (used a 6497 here for illustration, as the back is nice and simple). Of course if the red ring is perfectly balanced, it won't move about much, so it would need to be weighted on one side (green blobs on the image), with a heavier material. Much like the current outer parts of typical rotors.
The net result would be a whole lot of free space in the middle, to showcase the movement. Indeed the caseback could even "crop it out" and only display the inside of the movement.
Does this exist already ? If not, is it because there is an obvious reason that makes it impossible ?