I use penflip, which lets me download text as PDF, Word doc, ePub, HTML, .txt, or as markdown source. Who are you targeting?
It is an experiment as much as anything, and it is on HN just to see what people think of the idea.
However, based on my experience, if you need to get wide spread adoption, it has to be simpler that MS Word. Why? Because most authors are used to that. It will be the first point of comparison.
My $0.02