I guess this is another MMO topic, but an idea I've had (probably others) is this: When a person/group decides to go out on a quest or a mission. The gameplay could change to the point were it's almost like an entirely new game, but it still feels like part of the MMO. Say in some futuristic MMO, you go on a stealth mission, the game could become a full-fledged stealth game. Or you're in a clan and you have to retrive a certain artifact, the game would become some Ghost Recon-ish reconassiance game. Of course this would be really hard to implement into any current MMOs, but I'm just throwing around ideas for the future.

if you could actually make all the modes resonably polished it might sell but isnted of making your game everything you would do better to make it one thing but do it well