If I understand it correctly it’s basically community to community federation, so when you subscribe to a community it also pushes other community posts it follows to your subscribed feed. Those posts would still show up as those other communities. A community becomes not just a place to post, but also as a curator that vouches for other communities as well. You could even potentially have a curate only community like a lemmy best community list to get newbies started, or category level communities.