Well, I don't think centralising everything on lemmy.world, especially communities, is a good idea.
Apart from the single point of failure issue, I would imagine that there's an infrastructural issue caused by putting too many communities on one instance not unlike the load caused by a user with a huge amount of followers.
As a community is the source of "truth" it has to sync all the data to all the subscribers. Distributing this probably makes sense (??)