I just thought BSG would be the perfect story/whatever for a MMORPG.
1) It is set up so that all the interesting characters in the universe are pretty much divided up by military rank, which gives a nice "level system" without actually using grind or levels. Goals reached by merit and valor. This
also makes a very nice way to sort of lead into the game.
2) The fact that they are all struggling against an untiring outside enemy could encourage a lot of cool cooperative social dynamics (Humans could play the Cylons too, but I think most would/should be human) which is great for a MMORPG
3) The storyline for both sides is just perfect for allowing lots of action and lots of players without having to worry about mortality or overcrowding, while still not violating the plot
3a) Humans - Any number of ships could be out there and not know about one another, ever. (Ships/fleets = servers basically) And all of them have several thousand people on board the battlestar itself, if not many many more in the rest of the fleet, so lots of excuses for more people, or shifting you at the same rank to some other battlestar or temp/permanent demotion if you get "killed"/wounded or put in the brig - but only by a rank or two.
3b) Cylons - Cylons are just set up so perfectly, since 1) they resurrect when they die, so players can keep their achievements and die at the same time, all within the plot. They just lose their cover for awhile. 2) The whole sleeper agent thing and spies in general gives a wonderful way both to restrict people randomly who get to play the really cool Cylon side of the game in a fair way, and to mesh well with the whole online/offline part of a MMORPG. If you consent to the possibility of being a sleeper agent, and the game flags you randomly as actually being one, then Cylon players in high ranks can log onto your character while you are offline and attempt to sabotage stuff, etc. without you ever knowing about being selected (limited time frame, though?) Then you log on to find yourself somewhere strange (unless the controlling players are superb at what they do...) and you have to try and cover your tracks. If you succeed, you increase your parallel cylon rank, etc.
And high mortality rates within the storyline give plenty of excuses for letting people have the option to switch sides if they want to at important promotion benchmarks, etc.
4) Cooperation in battle with a chain of command sounds tricky, but could be really awesome if it works out. Higher ranks get control of more, but their commands only show up as objectives to those below, and don't physically alter anything in the short run (they do directly alter ranks in the long run, though). I cant quite think of any games that work like this very immersively, except maybe counterstrike on a small scale.
5) Since this ship is also forced to be a fully functioning society, there are plenty of opportunities to make the game fun for politicians and shopkeeper types. You could try to get command of your own civivlian mining vessel, etc. Even be a member of the press. All of which is simple enough to automate when the game first comes out, and which leaves tons of room for new content to be developed later.