For a much larger world, you would probably need to use something like World Browser, though there are some known limitations in regards to multiplayer. MMO-like games require a great deal more custom setup than a simpler level using level streaming as described above. I believe you’re correct about replication configuration not being solution to your problem; I misunderstood what you were trying to achieve.
I would recommend checking out some of information in this forum post, starting with Sean’s and ddvlost’s responses:
I’ll check in with a few developers and see if I can find someone who can give you some more insight regarding larger-scale multiplayer.