What functionality is missing? What is unsatisfying with the current situation?

  While it is possible to move an article from one world to another through the "special actions" box, it isn't possible to generate a copy in another world.  

How does this feature request address the current situation?

  It could be useful for many types of creators: if you create parallel worlds/timelines, if you create spin-offs/parallel stories occurring in different countries/continents/era, rather than have everything as a melting pot on a single world, you could only have relevant articles for your parallels/spinoffs and one "main world".   The articles would be easier to edit to fit one specific "world". Rather than have to copy every single box, it would be possible to only edit the parts which differ. It would also avoid having to create multiple copies of an article within a single world or have a single, overcrowded article.