So, if cross-posts are not showing up in my feed, then I have to actively look for cross-posts separately in the communities? How would I even know they exist? That’s still not what I want. In other words, there are two kinds of cross-posts: (1) redundant posts to overlapping demographics. I don’t want to see more than one of these. (2) commentary cross-posts. I want to see these as separate posts.
Sibling communities would hide (1) and not (2).
I like that you’re imagining new ways to do this. That’s what I’m trying to do too. This brave new world of community created multi-communities honestly sounds a lot like sibling communities to me. There’s the question of who is making the multi-communities, and to me the natural response is “the communities themselves”. There’s less user friction if a community is just already affiliated with a bunch of other communities voluntarily.
I think you’re forgetting the other half of the slogan: decentralized social network. You want to maximize decentralization? Disconnect from the internet and type to yourself on textpad. What we want out of the fediverse are the advantages of bringing people together, with the benefits of decentralization. No one wants decentralization as an end in itself.