I've fancied the idea, but don't think it will happen anytime soon. I prefer to have control over the different courses of my story. If I want the hero or heroine to have their fate dragged out, then I'm likely to axe someone's appendage that has that person reach satisfaction and thus end it (in my mind) prematurely. Yet, I am conflicted to do such a thing, since I feel it was designed for people to add on to stories they are drawn into.
I realize it's adaptable. I just don't think I would work well with it. Otherwise, I have a swapping story ready to go.
I must also echo KM here. At least with a story, upon submitting it, it's over and done, and I can let it collect dust and not worry. On CHYOO, it would evolve into something else. I imagine it would become something beyond my imagination. I just fear it would be for the worse.