I think original worlds work best for MMOs despite the success of some licensed ones. The big thing is that working within the lore of an established universe means that your greatly limited by it's history and what needs to happen, unless of course you decide to set the game in some future timeframe, or in the distant, unknown, past, but to be honest most IPs don't work well for that and doing it winds up causing it to lose what people wanted from it to begin with. Some settings with great amounts of lore behind them, such as "Wheel Of Time" work so much on "chosen ones", and predestination and everything else that there isn't a lot of room for adventuring and becoming an epic hero, because by definition nobody else can be as cool as the characters the stories are about or do much that is noteworthy. Moving things to a past cycle would basically amount to playing on 20th century earth, and moving things to a future one would basically amount to playing in an entirely different world so what is the point? That's a random selection chosen largely because it seems to be a popular choice for a world people like, but it's also conceptually a really bad one from the perspective of gamability. Of course at the same time a rabid, low-IQ, fan base can support even the most unlikely of things. I see the prime example of this being "Lord Of The Rings Online" which while not a bad game by any means in of itself, causes me to lose brain cells whenever I try and think about it and reconcile the books with the game. The biggest issue being that it takes place during "The War Of The Ring" which is where all the cool stuff happens, however those events open and close within the space of a single year, I tried to get into it a couple of times but when I say walk past "event quests" where I'm supposed to say plant seeds and then harvest them during the same event next year (or whatever) to finally get a pay off, it just absolutely fries my brain. Generally speaking there is no way someone should be able to start out as "Joe Peon" and then work their way up to epic hero material in the limited time frame of that story, and when I hear people claim they somehow managed to get more than 365 days of /played time it almost makes me want to cry. The very fact that so few people realize this though probably helps the game, given that most of the players despite claims to the contrary have probably never cracked a book, never mind actually read "Lord Of The Rings", having gained most of their familiarity from the movie series.... who your fans are, how desperate they are, and how many of them are actually big fans of the lore as opposed to the superficial trappings are all big factors. The thing is though that most really good IPs for this happen to be fairly obscure and there aren't the "Casual masses" to maintain them with inertia, anyone who campaigns for an MMO based off of the property is probably such an expert that they would rapidly be the ones to turn on the idea once the realities set in.
Me, I'll be happy if they ever decide to actually make a decent game with both space travel and on the ground components. The only one that really tried it MMO-wise is "Star Trek Online" as far as I can tell, and the quality, especially for the ground portions, is pretty low. Other attempts have been things like the "Star Wars" games that tried to put an action mini-game into an RPG. "Galaxies" at least deserved some credit by basing it off of "X-Wing" and "Tie Fighter" which themselves were based on the successful "Wing Commander", "The Old Republic" basically threw in a "Rebel Assault"-like tunnel shooter, and is just now deciding to try and recapture some of what "Galaxies" did by creating a spacefighter PVP death arena which has so far failed to capture my imagination.
If someone could make a game like ToR or Anarchy Online on the ground and have a space component like STO or EVE (very different playstyles mentioned intentionally) that would be perfect. To me not saddling it with someone else's IP would be a good thing. I play more STO than I should, but I admit even set in the future it irks me when people point out how crazily non-canon it's gotten (I mean really, really, out there), mainly because they are right. I mean when someone say flies by in a Tholian Carrier that has been partially assimilated by BORG technology and is mounting Elachi Disruptor weapons (a species new to the game) and is supposed to be a Star Fleet Admiral no less... it kind of hurts the brain and makes one wonder if they wanted to get that crazy why they heck they even decided to try and claim it was "Star Trek". The different playstyles and toys in STO can be fun, but really an open universe of their own making would have been better for them to go crazy with.
