all posts are just made in !lemmyshitpost@lemmy.world

At one level, I absolutely HATE the duplication that splits comments.

At another level, I recognize that splitting comments is most of the point of community. Making all people comment on all posts essentially breaks the entire concept of developing a community-specific culture of rules and norms.

In theory you could have each community "adopt" posts, creating community-owned discussions against universal posts. That would be OK. Then instead of cross-post duplication you could look at a single post and see all of the communities that have adopted discussion on it.

Maybe that's the solution.

A tagging-based social media is an interesting idea, but for something as discussion-focused as Lemmy, I don't think it'd be a good fit as a primary algorithm/sorting system. Individual communities are just too different, and often serve different purposes. For example, while political memes and non-credible defense share a lot of content, one is a more serious and focused on governments and systems, the other is absurd and comedic and focused on militaries and their equipment. Their comment sections need/have entirely seperatre rules and shouldn't be mixed. That said, a more in-depth tagging system would be handy for searchability and browsing.