Yes, that's what I'm talking about. I enabled that setting, edited the css in the shadow dom, and it only changed the appearance of the component I was in, not all the other components of the same type.

As far as I can tell, shadow-dom and web components are anti-tinker in that they don't allow users to play with the underlying definitions in order to learn how to use those technologies themselves. I think that will be a big barrier to adoption.