Tags are very useful, and Discourse handles them very well. For instance, I would subscribe to a “bitwig” tag, not to miss any topic about Bitwig.
This forum is still young. What about enabling tags? I’m happy to contribute some work tagging past and new topics.
For instance, #resolved is now a category. Are topics resolved supposed to be moved here? This doesn’t make much sense. “Resolved” could be just a tag added to topics resolved anywhere.
(There is also the very useful Solved plugin for Discourse, but I digress.) 
I’ll keep bringing examples as they come if you don’t mind.
Operating systems could be a useful family of tags: Linux, Windows, and so on. Discourse supports groups of tags, so it would be possible to have a schema like e.g. Linux / Ubuntu.
This would allow tagging bug reports. User specializing on i.e. Linux could subscribe to the Linux tag, be notified when a new Linux report lands, and help each other effectively.
In the opposite end, if someone is not interested in Linux bugs at all, they could silence this tag altogether.