Feature summary:

We would like the ability to create pages holding the comments when we post the comments. This would bypass the associatedpagedoesnotexist error when you post a comment for a non-existant page. We envision a flag that would be available to tell the API "Create a page if it doesn't exist" when calling cspostcomment

Benefit and use case:

To implement T193234, we would like Special:AllDiscussions to be a place to start discussions. To do this, we're creating a Discussions namespace that will hold discussions started on the special page. We expect these pages would be limited to a single comment streams topic initially and would host a single comment and multiple replies. The page could also be used to summarize the discussion later as a step in the documentation-improvement process that some discussions would merit.

This Discussion namespace is behind the $wgCommentStreamsUseDiscussions flag (which defaults to false) and neither the namespace nor the Special:AllDiscussions page would be available if the flag were not true.