Note that the “topic” here is essentially what I called the “title” in this other thread.
Also note that there’s also the proposal to have a separate discussion post type on meta. It is not unthinkable that one day we might want to implement threaded posts for discussion-type meta posts. That is, “answers” on a meta discussion would in turn get their own “answers”. So the possibility of supporting forum-type threads in the future, while not the most important consideration right now, should also not be dismissed completely.