I strongly support Adam's idea, and I add that a mul-wikisource could the perfect site to collect best coding/formatting standards and ideas, scripts, modules and templates to share them; this could be a great help for minor wikisource projects and an incouragement to KISS and to standardize practices for the major ones.
Really, my personal dream would be a unique, multilanguage wikisource just as there's a unique, multilanguage media container: Commons, and an unique, multilanguage container for structured data, Wikidata, for identical reasons; but this - I presume - can't be realized any more. What can be realized is, to remove any discouragement to upload into oldwikisource books in any language, to add a mul prefix so that books can be freely interlinked and to encourage to upload there multilanguage books.
Alex brollo