Expanding on your idea, I thought it would be interesting to have an MMORPG with multiple completely different clients. The easiest example might be in a future/sci-fi game, you have a normal game client for people moving around the game, and a Stock market client for people who want to play the stock market in the game. You could have a business simulation client as well maybe for shop keepers. Maybe a news website to try and bridge the gap between them all, but you could play one game (the stock market game) while never logging into the First Person "MMO" client but you're completely integrated. If you could think of a number of these different clients, I think it would be interesting.