The reality is that every server will have some local version of a bunch of the most popular things, and that will eventually reach a steady state with a tail. A few big ones, more medium size ones, decent number of small ones...
There's no point denying it, discoverability will be harder and communities will be smaller. So if you actually know of a really good community or magazine to point someone to, just do that. They can read the content without logging in. If they want to participate, then the server that they found a community they want to participate in is the obvious place to create an account, from which they can see everything else as you've said.
Little is being forced by the choice of server/instance, but that's not helping solve the hard part. The hard part is them finding what they need to find. They need a librarian, not a tech support desk. Tech people constantly assume the solution is technical... make the popular destinations popular by talking about them everywhere.
There's no point denying it, discoverability will be harder and communities will be smaller. So if you actually know of a really good community or magazine to point someone to, just do that. They can read the content without logging in. If they want to participate, then the server that they found a community they want to participate in is the obvious place to create an account, from which they can see everything else as you've said.
Little is being forced by the choice of server/instance, but that's not helping solve the hard part. The hard part is them finding what they need to find. They need a librarian, not a tech support desk. Tech people constantly assume the solution is technical... make the popular destinations popular by talking about them everywhere.