How are you imagining communities to work? Is this part of the dev plan? And is it a change to the blockchain or just a client-side feature?
I have an only half-baked idea that a Steem browser that allows you to look at all the posts tagged with A and B and maybe C, etc would form some kind of communities automatically. Maybe I want to read about goats but only from the homesteaders so I look at the posts with those two tags and if other people are doing the same, a community forms. I've seen this happening around the #steemitironchef tag, so it's not like multiple tags are needed, but it seems like narrowing things down would help. Also, a group of friends could make new tags for their use as a throwaway just to help filter other subjects -- like your #photography example, maybe.
Here is the repo that is being worked on... https://github.com/steemit/hivemind
was expecting it to be online almost 5 months ago