Hey, I'm the guy who started the .ml fediverse community. I started it with the Lemmy part of the network was young, and there weren't many instances yet. It's become a very active community, and I'm constantly amazed to see how much faster things move these days.
This has kind of been an ongoing conversation in some prior feature request discussions for Lemmy. One idea is that communities could consensually relay posts from one together, effectively creating a group containing Group Actors. This would probably cut down on duplicate content, but could create a larger surface vector for spam. But, I think it's an interesting idea.
I don't really have a full idea of what the best solution is. A Fediverse-specific instance similar to socialhub.activitypub.rocks could be a really interesting experiment, in that it would try to serve as a "Neutral Zone" between instances while sharing all kinds of news.
In the end, I don't really have much of a horse in this race. I think cutting down on duplication and redundant communities in favor of a more active shared space would probably have a lot of benefits, there's always going to be independent communities dedicated to the same theme on some far-off server. I'm not really interested in preventing anybody from starting their own.