So, the way that I figured it, you could have the !something@someserver concept, which I call groups (lemmy calls them communities), and the collision of those (say, !something with no server), would be called "regions" because they'd be several competing communities trying to use a shared resource. Moderation of a region would be a nightmare.

You could probably make a reddit-esque "multireddit" style view that represents the "regions" concept - just know that you are posting to a particular community with particular mods, in the end.