Doesnt the shadow-dom solve the problems with css modularity. You just write the css for your component, and it doesnt leak into anything else... Why do you need something like css-modules?
You gotta remember, Shadow Dom is a double edged sword, - while it prevents styles from leaking in, it prevents styles from cascading too. And sometimes, cascading was a good thing. Without it, you need to reapply base styles, and that's annoying. With this approach, you can compose component styling by declaring what to inherit.