Currently, we can use some viewers with the URL parameter ?viewer=. Example ?viewer=comment.
But these viewers have to been implemented with some templates inside the skin. Of course, they can be written in the Skin object, inside the database, so that I could add some dynamically.
But I would like to be able to add viewers like we add UI extensions. So we would be able to create a "xwiki-platform-comments" module, instead of having it in the default war.