Judging from the name "World+1" which has been suggested elsewhere on canny (https://openspacesocial.canny.io/feature-requests/p/post-reach-feature), it seems to be proposing a post which is attached to one community and the world. I will propose an expansion on this idea from World+1: the ability to attach a post to of communities. This can be implemented in the database in such a way that you can then "deduplicate" the post in home feeds, and prevents clutter from people reposting the same content in multiple posts.

Reposts can be used for this as well, but how they are identified and what additional features they have (like adding separate commentary or comments to the repost itself) will determine how they can be deduplicated. This isn't as simple to implement as just being able to attach one post to multiple communities.

The main concern is determining whether the GROUP By or DISTINCT or whatever SQL mechanism you would use to deduplicate on post IDs would be slow for the database to do.