Thanks jrista, that was clarifying. So that means that it has nothing to do with the design of the specific lens, since the diffracted wavefront already exists when hitting the lens. Criticizing a lens for onion-ring bokeh is therefore incorrect. Right?
I would indeed say "right"! There is no way the Otus, touted as such a high quality lens, and clearly seeming to be such a lens, would produce such "onion ringing." Zeiss should be sued if they allowed that...that would mean they used glass of poor quality with impurities, which simply couldn't be the case given how sharp the lens is corner to corner.
For comparison, here is a photo of some christmas lights on a christmas tree that I took years ago. I tweaked the focus of this shot to purposely bring out the effects of diffraction. You can clearly see the primary diffraction pattern, the large circular pattern that dominates the shape of each blur circle, caused by the lens aperture. (NOTE: The blur circles here also exhibit spherical aberration, hence the reason the outer edge is brighter than the center, which is counter to your standard airy pattern, where the center is much brighter than the outer rings).
You can also see the diffraction patterns caused by the obstructions presented by impurities within the glass of each christmas light. They look like rocks in a pond, causing additional waves in response to an incoming mechanical water wavefront.
This is definitely not the lens, it was the EF 100mm f/2.8 macro lens, an otherwise high quality lens (certainly not as good as the Otus, but very good otherwise)...notice that each light exhibits a different pattern of obstructive diffraction, where as the primary circular diffraction wave caused by the aperture exhibits the same in each light. Two causes of diffraction converging in a single image. The "warping" and inconsistent gradient/rainbowing and larger but softer internal rings of each blur circle is also due to the glass of each Christmas light, not the lens. You can tell because those aspects of each blur circle change per light.
If the nature of the wavefront and it's diffraction pattern changes with each light source, then the issue is most likely rooted within the light source, itself. If the nature of the wavefront and it's diffraction pattern remains consistent across light sources, then it is likely due to either an obstruction within the light path between the source and the lens, or the lens itself. Obstructions within the light path will remain consistent themselves, but may change position within the blur circle of each light source. Diffraction effects caused by the lens itself will always be exactly the same for each blur circle in the image...usually, if you have focused right, that will present as a circular waveform that should be pretty uniform and otherwise clean in nature.