I imagine it like friend requests between communities: x@instance.a, all-about-x@instance.b and x-is-great@instance.c could send each other friend requests and merge into one federated meta-community about x. Then if one instance goes down the other two are still there to keep the meta-community alive, and if one goes rogue the others can just unfriend and keep going without it.
The nice thing about manual federation is that the communities don’t have to have exactly the same name, and the mods can keep malicious or troll communities out. And ofc you could still have client-side control if you want to, e.g. add or remove a community just for you locally, or create your own local meta-community.
An app to manage important config and unit files (fstab, hosts, sysctl, systemd units, …), and present them as settings menu or editor with auto completion and tooltips. Kinda like how VSCode handles settings, where you can use the GUI or a context-aware text editor.