I think that tags works alomost like "substeems" (like subreddits in So all we need for that is a tags filter.

Yes and no. Because posts can have multiple tags it is easy to "spam" popular substeems, unlike reddit.

Creating viable content subviews or even more so viable subcommunities as is the case for many subreddits requires a bit more or different functionality.

Maybe we could delegate some of tagging work to curators? I mean they should have an option to upvote or downvote some tags in a post. And then these tags will be sorted (shown) in such order as they are preffered by voters(curators).