I wonder if it may be simpler to write a site that outputs nothing but RSS/Atom. If user participation is allowed, they can contribute by using PUSH with JSON or something similar. I'm sure the vast majority of mobile apps already function in this fashion (maybe they just use some proprietary format to get the content).
The problem with RSS these days is that many, many websites use RSS as a way to get people clicking on their site and don't provide full-text feeds.<p>Hell, you can put in ads as well as metrics code into RSS feeds, that's just not a valid excuse to not provide full-text feeds.