I love single file components. I used Polymer before React and that is the thing I miss the most. I've also been using CSS-in-JS for the same reason. I landed on JSS for now, but I'm hoping we'll see a solid scoped CSS solution soon.
I think I'd prefer to have a component directory with HTML, JS/TS and CSS/SCSS files in.
If you're using vscode add plugin "Template literal editor" and you get full intellisense on the CSS too!