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/communityname@instance.name” on it so you know which community the comment was originally posted on.
Maybe the solution is more on the client side. An app should be able to let the user add communities from different instances and present them as one, maybe even merge comments from identical posts etc. Then if the user gets fed up with some instance not moderating or spamming, the user could then just remove that from his multi list.
Technically there’s no way to please everyone on this, but there’s also no reason why the apps couldn’t present a meta-view of what is actually happening across instances, if that’s what the user prefers. Most users don’t want to see the gears turn.
In addition to the user experience it would also minimize any “damages” from any instance going down, because the multi list would remain active as long as any of the instances are up.
Maybe you can subscribe to “news” and it gives you a submenu where you can tick which instances you want to include in your own selection of “news” community.
It still leaves the question of how it deals with crossposts of the same article to multiple instances.
You’re absolutely right! Easy and simple fix, which does not require any more decision rights, or extra responsibilities, being given to the instance operators.