That's an interesting piece of history.

On the other hand, a circular image is just as limiting as a rectangle. The photographer has to pick what to show, what to eliminate. A landscape painter has to do similar, but they have the choice of adding/removing/moving elements. All we get to do is move around, change viewpoint, maybe change depth of field - or wait for the view to change.

BTW, I've noticed that centering a subject and radial symmetry seems to work well with a circular image - sort of the way you'd use perspective distortion in a wide lens as a design element.

https://www.flickr.com/photos/nationalmediamuseum/sets/72157606845434332/

Also, going into the sensor box and adding some mirrors "just because" is beyond cool. I'm no stranger in there, clean my own sensors, have added might sky filters directly over the sensor - but I would have been intimidated by this.