I submit that "supervisor/user" isn't an implementation of "rings", plural (and it's got to predate Multics by a lot, but I can't quickly prove that), and that SMM is something entirely different. Hypervisors and there use really aren't comparable to Multics Rings.

A couple of minutes with Google only found hints that confirm my memory WRT to AMD64 and rings, and/or Intel not copying a segmentation feature added to later versions of AMD's chips.