Yes each blog topic would have a comment topic in another category/sub category.
I am wondering though if a similar ko Nd of iframe idea might work. To create maybe a div that will display a topic within a box. More or less a kind of iframe. Similar to how we can use CSS and TC to influence how a category displays.
Category permissions in this regard the blog topic would be similar to Moon’s suggestion of the journal plugin. Only the Author can post & reply in the Article category. The comments say in the final post would be an element showing window to comments in an interactive iframe idea.
Alternatively could likely just use code similar to serving discourse comments on something like ghost blog. But I think it could likely be made to look & work similar to media sites with comments section.