What I love about this approach is the inherent duality of every document. I applaud this multi-modal approach, and over the years I've built a few such systems myself. But I have to admit the whole idea troubles me somewhat. On the one hand, it's a good thing that the Web, e-mail, and news are different media with different strengths. E-mail is best for offline use, and for most people it's the natural way to communicate.
News handles the threading that e-mail never got quite right.
But there are two dilemmas here. For implementers of multi-modal systems, it's a major challenge to support three very different interfaces and protocols. For users of such systems, the problem is that no single interface unites all the best features.