I think it should be nice to have the opportunity to create topic link à la Reddit/Hacker News. A user can submit a link by creating a new thread and just enter an URL in the Title field and add (or not) a comment/Tag in the Post Content/Tags fields. The new thread appears in the thread list and others users can comment the topic link as in an usual topic.
Admins can decide to allow this feature or not.
What do you think ?