I believe that all templates of article should have an additional section: Writer information. This would allow the storing of information relevant to writers, or for GMs in a campaign, without revealing it to normal viewers or subscribers. An example usecase for this would be a merchant's inventory in an RPG campaign, or notes on collaboration with other authors that are less... content focused than what would normally be appropriate for a secret (see below).

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

Currently, the only way to have GM only content in a public page is by creating a secret and not sharing it with any group. This is clunky, as secrets don't have quite the editing capability of a normal section (For instance, tables in secrets can only have a maximum of 6 rows in the graphical editor), and are not displayed on the page without hitting the tab. Generally secrets are only well suited to storing small pieces of information, where having an entire hidden section would permit the storing of larger amounts of information in a seamless way.  

How does this feature request address the current situation?

By adding an extra section, this allows display of meta and gm information in a manner that makes this information a first-class member of a page, rather than the current option of either making a second page and leaving it private, leaving the whole page private, or trying to do the same with secrets.  

What are other uses for this feature request?

I imagine there are many usecases for writing down information that is relevant to only authors in a way that's more obvious on the page than a secret, however no specific examples come to mind as of time of writing.