I don't think so, at least not from non-professional content producers. There will still be a desire to have an easily written, shared, and rendered document up

I don't think so, at least not from non-professional content producers. There will still be a desire to have an easily written, shared, and rendered document upon which you can give your thoughts. HTML has always been best at that, and will still be good at that in the future. The only contender I know of would be markdown, which fulfills many of those needs while being even easier to write. Its greatest pitfall in a contest against HTML is that it is by design non-standard, as it is meant to be a pre-render stage document, and presumably your render stage will smooth out any non-standard markdown elements, giving you a standard document in a format like HTML.