In his blog, Kevin Werbach recently referred to an article by Helen Cheng - i'm a resident of second life wut?
I like the idea of her split between creator and consumer, though Kevin rightly notes that people are not simply one or the other. That said, I do think the balance between the two favors "consuming" for the majority of people.
I would question the thinking behind a completely open-ended virtual world - one in which you logged on and were free to do whatever you wanted - for the simple reason that you would be drowned in choice. Too open-ended means that there are too many paths open to you and unless you enter the world with an idea of what you want to do (i.e. a predetermined direction) the potential to do anything can make you want to do nothing. Generally people want choice, but they also need that choice to be manageable - limited, really. Not limited in what you can do, but in the number of options open to get to the desired end result.
Much more attractive to the general consumer is participation in a generally pre-determined world that allows for varying degrees of customization. WoW, I think, comes at the low end of the customization that is possible within a fixed virtual world. Being able to choose my avatar's hair color (from limited choices) is pretty...well...meh. Customizing the UI through addons is much more important. Though I don't develop addons myself, I do use them, and by using them I personalize the game - make it mine. Which is what I think is the draw underlying the Second Life appeal to creators.
What I would love to see is a virtual world that successfully balances (A) a pre-determined world with solid structure (interface structure and content structure) - where the user takes a passive attitude towards creation - and (B) a world that allow the user to make the experience as personal as possible - where the user takes an active attitude towards creation. Allowing user customization that affects only the user is fine, but if that customization is external within that world (i.e. affects other users) then the potential for game balance issues arises. Still, I would love to see people tackle this.