You’ve been reading about Discourse’s fourth trust level, haven’t you? I should warn you that there are known weaknesses in its approach.
One of the obvious ones is that a TL4 user can’t break a mega-post in half. The only way I know of is for a moderator to edit the off-topic chunk out, make a new post elsewhere, and reassign the post to the OP. And only moderators can do that.
The other big downside, inherent in any curated approach, is a feeling of lost autonomy. Kind of unavoidable, since giving you power is synonymous with giving you a system that you can game, but feelings of powerlessness are exactly one of the things you said you wanted to fix.
Taxonomies are not neutral. This includes whatever rationale the leader in question uses to decide if something is on-topic.
In spite of the fact that I think this is better than Reddit’s approach (notice that I have TL4 on here, while my Reddit account lies deleted and burned), it’s not going to completely fix the growing sense that individuals don’t have the ability to shape rust’s direction any more. Because they don’t. And any process, even a manual one, is going to be dominated by whoever puts in the most time to deal with it.