I wonder if the "secure distributed persistent communication" protocol developed by the E folks could be used to implement a virtual world running on a network of clients. I.e., one central server would send a client some model of a room, and the trust layer would prevent that client from moving walls around. (I'm being handwavey here because I'm not familiar with either E or MMOs, but maybe someone else can be inspired by this.)

http://www.erights.org/