This isn’t specific to Blender’s GE but The Laws of Online World Design will probably be interesting for a lot of people here if they haven’t already read it.
Also of (possible) interest is the MUD-Dev Archive which can now be downloaded. MUD-Dev was apparently the main location for high-level technical/design discussion for all forms of online world design for a long time. I haven’t looked at it much yet, but I believe it mainly covers MUDs, although designers from games like EverQuest and other graphical worlds participated and the archive was the source of rules in the article I linked to above.
Enjoy!