There is the Fediverse, and there is kbin.social. I'm not even sure how to see what niche communities are out in the Fediverse. You'd have to go through each instance to see what magazines/communities (these are referred to differently in different places) exist out there. Is there a or could there be a directory of sorts to list your magazine/community so that others can find it?
I feel confident in saying we should not be planning to host every single community on kbin.social.