I was just thinking about this and how nice it would be to have ability to user tag or mention someone on individual posts, even if you're not post author /creator, which could potentially save time and direct persons to helpful threads without creating new replies with links to other threads all the time.
If you're reading a thread and want to help the person out, and you know of a useful thread that might help them, rather than just post a reply in their thread linking to another thread that's possibly helpful, you could just user tag or mention them on the first post in thread, or 5th post in the thread that's possibly helpful to them. It saves time, and acts as a "You-who, here's a helpful thread for you."
The user then gets notification of user tag or mention and goes to thread you're "poking them on shoulder for their attention" wanting them to see. Maybe have the user tag or mention auto expire after 24 hours or have it only disappear when user you're tagging on mentioning acknowledges it. Which helps save on database data storage etc. The user tag or mention is a just a temporary "attention getter" or "poke on shoulder" to get the person's attention.
Might help save on creating new single lined replies basically just containing links to other threads. Although downside might be no record of where the user found helpful threads for record keeping purposes and you might also have 50 threads with no replies to it, because users were mentioned/tagged in threads containing answers to problems and then have no interaction / discussion in long run. But in some cases might be nice to have the feature.
Edit: Or maybe better as plugin.