This sounds like your talking about Storygaming, a concept that I engage in on a site dedicated to such things, and where a handful of aspiring writers work together to better their writing. You idea is nearly identical, save in a Storygame, the readers make their own suggestions rather than you giving the options, and those are what's voted on. Your version is a bit more restrictive, still relying almost entirely on your own imagination rather than giving the readers an actual hand in the creative part of the process, but as I have noticed in RPers the distinct lack of such motivations, I see your way working better here. Don't get me wrong, there are a select few RPers who are, and please don't hate me for this, on par as far as creativity and actual writing talents go, but over all I have found such exceedingly difficult. Not many people feel at home on the other site I spoke of, mostly occupied by writers, and those who seriously aspire to be.

All in all, I wish you best of luck in your endeavor, and if you find you enjoy doing this, please feel free to shoot me a PM about the other site I spoke of :P