As someone who has opened and run an original-theme sci-fi MUSH, I can tell you that @Scissors and @FirePuff in particular are spot on, with an original theme, there's no way to give enough shape to the world that enough players will feel comfortable in it to RP without looking over their shoulder.
Some will forge ahead happily, expanding the setting in very themely directions. Some will forge ahead quite happily, expanding the setting in wildly unthemely directions (that they didn't know were unthemely because either it wasn't spelled out anywhere, they didn't read it, or they didn't care). Some will find one thing they feel comfortable with and RP in that niche forever. Some will ignore the setting and play their relationship dramas. Some will look at the copious setting info that has been provided and get turned off (either by elements of the setting or by the amount of information available). And some will look at the setting and try to break it.
If you can find a way to encourage the first and third groups (themely expansion and niche play), tolerate the fourth group (relationship), redirect the second group (unthemely expansion), and discourage the last group, you might be able to get enough people comfortable enough in the world that it can become self-sustaining. Ideally, you would be able to do this simply by how the information is presented on your wiki, and how it is presented (a "suggested reading" group of 5-8 pages is a good start, I think), but generally it'll also be by positive reinforcement toward those who make themely contributions to the setting.