Will themed virtual worlds be attractive?

As I’m pondering the question of whether themed virtual worlds will be attractive or not, my mind is going in all directions, so I’m writing this out to get some clarity. The different issues as I see it:
1. Second Life, the VW with the most hype, is not themed, but has themed aspects (furries, trekkies, etc… there are many)
2. Should I differentiate VWs and MMOs? MMOs have thus far been largely set, not flexible in terms of user control. You are there to play the game, not alter your surroundings. (please take with a grain of salt, I have not played many MMOs or spent much time doing so since the MUD, something I need to change)
3. Perhaps the answer to my question is, “of course they will be attractive to small groups (relative to the population as a whole), there is no need for another ‘catch-all’ VW like Second Life.”
4. Seems like there were more… I’ll add them as I think of them…

I’m not here to answer this now, just ask the questions.