With almost all things it is very good to test something out. An MMORPG that simulates a real-world economy could help us try our ideas in a real-world situation. It could also stimulate the early Ethereum ecosystem through giving us reason to spend our ether in the first days after the release. The MMORPG world could also benefit from the Ethereum project through decentralizing their games. It would be interesting and useful for collaboration between Ethereum and MMORPG worlds.
I'm curious what other people think of an MMO that uses Ether for things like it's currency, it's networking, or it's database.