What I've read so, it looks interesting.
Having tags would help constrain a proliferation of high-level topics. The plugin enables the creation of a page that lists existing tags (users can look for an existing, relevant tag before creating a new one), and enables possibility of tracking discussions around subtopics and keywords.
It might be possible to restrict the creation of new tags to particular categories of forum membership, should that be desirable. The code is up on GitHub, so our resident code-monkeys can have a look over it and offer suggestions as to improvements.
It's still being developed, but as an official Discourse resource, it's probably going to be less likely to bork your set-up (considering the admin side of this) than a completely custom job.
I like begin able to tag substantive posts in forums. It makes them easier to find for everyone. A couple of simple policies, and they also should be manageable from an admin's perspective as well. The Long Long Ago when I was a BBS, and later a forum, admin myself, this kind of secondary sorting regime helped reduce complex navigation significantly as sites grew and developed.
(On one BBS, we developed a matching set of admin-only reserved tags for flagging good posts, or problem users, or conversations that had drifted off topic, etc. We had a pretty good userbase, who helped each other out - the admin tags generally led to more experienced users bringing others back into the fold through the community.)