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

  To put it simply, the current manuscript system does not allow for changing the world in which a manuscript is labeled as taking place on. If you create a manuscript on world A, when you meant to put it in world B, it is impossible to move it to world B.

How does this feature request address the current situation?

This feature would be the same system used for articles: a drop-down menu with a list of your worlds. You select one of those worlds and click move. The manuscript would then be moved to the correct world.  

What are other uses for this feature request?

This feature could be expanded by allowing for the ability to move chapters or scenes from one manuscript to the other. This would be great if a chapter did not fit in one manuscript, but fit perfectly in another.