On the one hand, the idea of mixing all these messaging formats together sounds like it might be a confusing mess -- a Google Wave-level UI disaster. As he points out, these media have very different usage patterns that may not turn out to mesh that well.
On the other hand, saying "Facebook should just do a beautiful, elegant implementation of what everybody else has already done" is a very low-risk strategy. It doesn't innovate or solve any new problems. As a strategy for an industry-defining company, this is a route to irrelevance.
So is it better for Facebook to risk failure, or risk being boring? I have to say they've recovered well from failure in the past (Beacon, early mis-steps with news feeds), so my vote would be for the gutsy, risky, change-the-game strategy.