I love the idea, but I suspect that most people writing the sorts of content that could benefit from this wouldn't take the time to break down their work in a way that would take advantage of the layout.
If it's (a), that's basically what sites like Slashdot and Reddit already do for desktop users.
If it's (b), the obvious question is how you algorithmically filter text to only include the pertinent information (the given example is almost certainly hard-coded), which doesn't sound like a simple question to answer.