I’m a G+ refugee, and this suggestion comes from my extensive use of the COLLECTIONS feature on that platform. Now, I don’t want Diaspora to be a G+ look-alike, but I can see an advantage in adding it in Diaspora.
Diaspora has ASPECTS, which is handy in creating a specific audience based on a list that the user creates. The only problem with that is that you may not know at first what another user is interested in. Suppose say that one of your aspects is Whovian Stuff and you post about the TV show Doctor Who in that aspect. But you might not know who’s into that and who isn’t, and unless you specifically add someone to an aspect they won’t see those posts. That could be a good thing for them if they’re not into Doctor Who and don’t want to see a plethora of posts in their feed. But either way they won’t know about those unless you add them on the list.
The COLLECTION feature in G+ works in reverse. You create a collection and give it a name, a cover image, and a short description of what it’s about. You also decide if it’s automatically subscribed by someone who reads your posts in their feed, or one that someone has to subscribe to first, before seeing any posts in that collection.
Other users have a couple of options they can do: subscribe or unsubscribe from a Collection. Suppose someone in your feed creates an automatically subscribed Collection called BIG PHOTOS OF SPIDERS and you’re an arachnophobe - you can simply unsubscribe from that collection and never see it ever again. But likewise someone might create a DOCTOR WHO collection is not initially subscribed to. You discover it by searching the list of collections and subscribe to it. You’ll then see that collection in your feed, even you don’t usually see owner’s posts in your feed (and you can always unsubscribe later). What this system does, is allow a user to post to a topic, or a range of topics, in one group, so that those that are interested see those posts, and those don’t, won’t.
Of course a user in Diaspora could use a #tag, but the post is still going to be in an aspect which will additionally affect who sees it and who doesn’t.
Perhaps a Diaspora version of this would be a DIGEST. A Digest would act like a relay for a users posts without the reader having to subscribe to all of the posting user’s posts. A DIGEST would be set up with a Name, short description, and a list of tags reflecting what its about (and maybe an image, but that’s not essential. Any user could search the list of Digests by digest name, description, or tag. A user would click on a Digest entry in the list and see the digest posts, and/or subscribe/unsubscribe to it.
Just an idea. I expect this to be shot down for reasons that either something similar already exists, or other reasons that as a newbie here, I’m unaware of.