Hi jbehlow!
My mother has a 14k solid gold band that is ~10-12 mm wide, she has never owned a diamond in her life and wears it by itself. My MIL has a 1.5c RB diamond set in the center of a gold band that is ~8-10 mm wide...I''ve never seen a really wide band stacked such as your picture shows, but I think it looks great! Do you have a face-up pic you could show as well?
My WB is two rows of invisible set princess stones and is about 5mm wide, and on top of that I wear my 1.5c RB solitaire--it''s about 2.5mm, so ~7.5mm total width on my finger. I have long fingers, though, so the rings cover about a third of my lower finger, if that makes any sense. I have often considered purchasing a 10mm+ plain platinum band to wear by itself or with my solitaire someday...I love the look of a really wide wedding band.
I also love those Hidalgo enamel and stacking rings...I think it''s a great look and can imagine wearing one "main" enamel ring with 2 "stackers"--one on top, one on bottom.