Feature Suggestion: When posting topics in certain categories it will tag certain groups

This can help if an admin or moderator might need some feedback or help on something, and they made a category for it. Every time a topic is made in that category, everyone in for example an Admin group would get tagged.
Would this be kind of useless?
Or am I not thinking broad enough?
Could you do sort of the same thing by just changing your preferences in a specific category to tag you whenever a new topic is made?

You need to be a bit more careful here with terminology. I think you mean @mentioned

What your users can do is watch the category, then they will be notified for every new post in the category. They can even watch only first posts.