Nah, the only categorization that really needs to be done is by topic. It's easy to tell if something is, say, a tech article, or tech/programming, or tech/linu

Nah, the only categorization that really needs to be done is by topic. It's easy to tell if something is, say, a tech article, or tech/programming, or tech/linux, based on source and keywords. If your algorithm did that once per item that's in anyone's feed, everything else is refinement. Ideally, a human won't need to touch it at all. Even if the machine gets it wrong, it could be corrected with a "this is in the wrong place" button. In any case, an article shouldn't rise too high in any category that it's not relevant for.