Ernest Adams has, and he's not that pleased. Speaking to a crowd at GDC Europe, Adams said that the biggest problem in MMOs is that there's a disconnect between what the game tells us it's doing and what is actually happening. Mobs can never truly be "killed" since they respawn; NPCs don't perform any promised actions after you complete their tasks; and quests can be abandoned without any consequences.
Adams feels that player actions should be able to change the world in a real, significant way and be permanent (including the possibility of, yes, permadeath). Player choice should trump developer intentions, he says, quests should be unique to each player, and the game should ultimately have an ending.
Using the concept of a fictitious MMO called The Blitz Online, Adams hypothesizes how this might be accomplished. The game would take place during the attacks on London during World War II, and players would have to take action to shore up the city's infrastructure and defenses lest the situation grow worse. If enough players pitched in using their various skills, morale in the area would increase and the Nazis would eventually give up the attacks, causing the "win" condition for all.
By focusing on player choice and a dynamic game world, Adams hopes that the experience would become much more real and personal for players. However, he admits that such a project might be a long shot: "I realize this game breaks almost all the rules."