Thanks for the link. It is interesting that it is about SWG because that is the first MMO I played. It is also where I learned most of what I know about MMO server software. One of their programmers wrote an article about 10 years ago, detailing how their server software works. The main idea is that they were able to dynamically split up a planet into multiple servers and change it automatically based on server load. Very cool stuff.
Yesterday, we spent all day getting a 20km by 20km world composition map up and running for an upcoming MMO title. The map was made up of 16 2km zones where the landscape and other actors were separated into multiple sub levels. One of the big issues with World Composition is that the server is always running all of the sub levels. This would be horrible for performance. So I modified the Unreal engine code to allow me to filter which sub levels load on the server from my server system. This allowed us to load 9 landscape zone sub levels (the 1 we are in and the 8 surrounding ones) at a time and only load the actor sub level for the zone we are in. By doing this we were able to get the dedicated server to run in less than 400 MB per server instance and keep the client running at 60 FPS (on a mid-grade PC with old video card). The client was properly streaming levels in and out to help with performance. For open world systems, this seems like the best solution right now.
If anyone wants more information, join our discord channel and we can chat.