I was looking at something like this (a hierarchical index of existing lemmy communities) a while back, but discontinued the project when I realized just how slowly I was progressing and that I didn’t want to go through the hassle of setting up to crowdsource it. Lessons learned and questions asked:

1. Organizing hierarchies is hard, and they do have to be organized from the top down if you want to come out with something good—the number of categories at the topmost level has to be kept small for the hierarchy to remain usable. (The important, widely-used groups on Usenet always fit under either the Big-8 hierarchies or alt—anything else was small, regional/local/server-specific, or non-English. Usenet’s hierarchy isn’t really appropriate for Lemmy, I don’t think—it’s kind of suboptimal even for Usenet, with the alt hierarchy containing a bunch of stuff that should be elsewhere.) I think I ended up with about a dozen top-level categories during my experiment.

2. Categorization can’t be usefully automated (at least, not at present). All categories have to be assigned by a human if we want them to make sense. At most, uncategorized communities can be auto-dumped into an “unsorted” top-level category for examination.

3. Many communities don’t fit neatly under one category. Usenet’s hierarchy was strict-tree, so everything had to be in one, and only one, place. I decided to allow three places in my experiment (plus a language marker), so that, say, a community for an amateur softball league in the greater Toronto area could be placed under Lifestyle and culture > Fitness > Sports Leagues > Softball, Sports > Amateur, kids, and local > Softball, and Regional > North America > Canada > Ontario > Toronto. So that’s a thing that any categorization initiative has to think about.

4. Is it worth noting issues other than “NSFW” that may exist with a given community, since a human has to be looking at these anyway? This could be anything from laissez-faire free-speech-absolutism moderation to the presence of photos showing nipples in a nonsexual context (a breast-feeding community, for example).

5. Should communities on servers that almost no one federates with (lemmingrad) be included? Communities with illegal material (piracy links)? Communities with really illegal material (CSAM)? Where does the line get drawn?

6. This whole thing is a good-sized moving target, so a crowdsourcing effort is necessary.

7. Not all communities present enough information to make them easily categorizable by someone who is not a member.

8. Should a line be drawn regarding category abuse? The Usenet alt hierarchy contains a lot of what I would characterize as joking juvenile vandalism (alt.newgroup.for.fun.fun.fun is a SFW example of the kind of thing I’m talking about—many of the others have NSFW-ish names). Is this even worth guarding against?

Those who forget USENET are doomed to repeat it forevermore…

Up until now, social containers like groups, communities, or subreddits on all the largest social networks have existed as fundamentally separate locations on a single hierarchical level.

“Up until now”… Uh… no, Usenet… was the open standard for social media. Created in 1979. A foundation of the Internet. Just as much as e-mail was.

alt.tv.simpsons
alt.tv.futurama

So… multi-communities (mc) that can include multi-communities?

If you wanted to get more fine-grained to allow filtering of busy communities (c ), you could add tags (t) to posts so they would be contextual (it would be able to distinguish between rock music and rocks, for example) and could then also be added into multi-communities.

So if you were interested in dinosaurs, you could have an /mc/EarthSciences that contains /mc/Geology, /mc/Meteorology and /mc/Palaeontology and inside the last one you might have /mc/Dinosaurs which might include a few /c/Dinosaurs as well as /t/Dinosaurs, the latter scooping everything else up. /mc/Dinosaurs may also contain /mc/Velociraptors, /mc/TRex, /mc/Spinosaurus, etc, etc.

It would be easy enough to add tags semi-automatically as each community could define relevant ones that’d trigger on keywords,.so a /c/Geology would have /t/Rocks suggested triggered by “rock” or “rocks” (where a /c/Music might pick up “rock” and offer /t/RockMusic). Someone posting would be offered the automatically generated tags to accept, remove or add others from a drop down menu. Posts without tags get flagged for moderators to look at.

Not sure if you’d allow users to create the multi-communities or leave it to the instances admins and/or mods or have a half-way house where users can create them and suggest them to admins.

Gentoo Linux agrees… the very root of the concept of “federated” comes from Usenet, which did not have a flat hashtag style group, a flat subreddit /r/name /c/name kbin magazine convention.

I feel user defined multi communities will get lemmy pretty close to this. Multi level hierarchical feeds could then be achieved by allowing the user to include a pre-existing multi-community in the sources of another, which would just be a front end thing, nothing new on the backend.

Beyond that, users and communities can self organise. Users can share and recommend multi coms while communities can do the same for other communities they seem themselves connecting with. Again, more front end stuff that should be pretty straightforward for sharing and importing multi com definitions, which would all just be lists of communities.

So… Like Tildes?

Wikipedia has its hierarchical categories, for an example that is already working. More historically, the librarians have the Dewey decimal system and the subject classification system.

But it’s a good idea and may give the fediverse an edge until reddit copies it.

Now this has some potential! I have something for my nighttime reading list! Great post!