Original idea and related discussion is here:
Basically, allow an admin to change who is listed as the author on a piece of content. This would be useful for internal communities when an author leaves the company. I have found that many times, even if a go to person is named in a document, the reader assumes they should contact the author. And when the author no longer works at the company, that causes confusion.
Another use case: When the author of the content leaves or takes a new position, the person's replacement wants to be notified if there are comments/changes on ALL of that person's documents. Forcing them to find the content (for which there is no good method, see idea here: Ability to export content list for a user) and then sign up for notifications is tedious and error prone.
Another reason this is important: People often post content right up until the moment they leave the company. Then, when others update or comment on the activity after they leave, what shows up in the activity stream shows that owner and their grayed out profile avatar. From a usability standpoint, it is important for people consuming the content to know who to contact if they have questions, and not being able to change the author (or assign a separate owner) is problematic in many situations.