Communities on different instances about the same topic should have the option to essentially federate so a post on one appears on all of them and opening any of them shows you the comments from all of them. This way when lemmy.world is down its not a big deal because posting to any news community federates to all of the communities instead of barely having people see your post. Federation could be decided by the community mods and the comments can have a little “/c/[email protected]” on it so you know which community the comment was originally posted on.
I like the idea of a distributed community where everyone can see posts from any other instance they federate with.
You could have two types of community, one federated local and one federated global, and the former acts like current communities, and the latter would act like a big pot everyone throws stuff into, and local instance mods could set which instances to accept and deny posts and comments from, and which instances to federate moderation actions from