I actually love this idea. I'm on a federated service, why do I need to go to 3 meme communities on 3 instances when I could go to "meme" and see all of them?

Crossposts from within the cross-feed could be automatically hidden to avoid showing the same post multiple times, and then we just start spreading the word to crosspost instead of reposting. I think the only issue is that this would definitely be better to implement client-side because AP is just a protocol to move data, whereas this requires checking too many user-defined variables to make it idiomatic easily. I could be wrong though, I don't know the AP code very well