User blog comment:BertH/Darwin - The Next Evolution of Wikia/@comment-4674838-20130823022803/@comment-11733175-20130823084203

I believe they're waiting to see how this works before rolling it out anywhere else, such as user css or Mediawiki:Common.css.

Ace, which is what they've used for this, supports a variety of languages. I know the Wikimedia version supports js, so it's certainly possible.