I like the idea behind this and other projects like it, but I have one main issue with it/them:

It isn't trivial to share presentations, which is something that most people will want to do. Sadly the fact that you can build a presentation in HTML (and that people can look at it online) doesn't outweigh sharing a PDF. Don't get me wrong, I'm all for lighter more flexible solutions (which html is), but the market as a whole generally isn't.