But to your question should all CSS be in JS? I'd say no, that wouldn't make sense. Clearly site level CSS should remain in a file and can be just included in a link tag normally.
The CSS being moved into JavaScript would be just that CSS used by the objects. This is how OJ Objects have no dependencies. The CSS for the YouTubeVideo, or Tab control, or the TwitterButton is included in the objects themselves. So definitely imagine still using CSS as you do now, but pulling out only the css needed for the reusable components into OJ Objects.