There is a lot of potential in Wikisource, but it depends heavily on the ProofreadPage extension and it has several bugs that are reported but don't get fixed.
ThomasV is the main developer and perhaps he is the only maintainer? It would be in the interest of the Wikimedia Foundation to assign a salaried developer or two into developing a more robust framework for Wikisource, either by improving the existing extension or by integrating some or all of its functionality into MediaWiki proper.
People everywhere have a need to make some PDF (or Djvu) document available on a website, page by page, with the ability to add categories and talk pages. This ability is what the ProofreadPage extension adds to MediaWiki. In my mind, it is as essential as the support for uploading JPEG images and automatically generating thumbnails. Adding multipage documents to a wiki should be a far more common need than adding mathematical equations.