I understand the idea of keeping them separate and not forcing them to a single instance since that defeats the purpose of decentralization. But from a UI standpoint it would be nice if you could a user could create multi-communities or groups where the content from all the similar subs you put in them show up in a feed. So if say I want to see c/aww I can have a group I created with content from aww@lemmy.ml and aww@lemmy.world and awwwwww@sh.itjustworks etc.
If an instance dissappear or goes rogue and gets defederated that content just dissappear. I don't think that breaks the decentralization idea but solves the user problem.