The new-stuff, while great for styling, isn't all that relevant for scripting. nth-child, say, is often (though not always) simply an indexing operation on the return value of querySelectorAll; and in general you don't even want that since usually you have a specific element in mind and have labelled that element with a class to find it.

I don't support IE8 anymore, and use CSS3 liberally in the actual css, yet I can't think of more than a handful of cases I used the selectors from javascript, certainly none of them critical. Do you actually use this?