"he took it upon himself to create a new kind of communications system for Facebook that could relieve some of the pain, bringing project management and communication into a single application"

There are tons of these things floating around, e.g. Basecamp from 37Signals

The thing about email though is that it's (a) free, (b) distributed not centralized (unless you choose to use a centralized service like gmail), and (c) the mental model is totally accessible to all including my grandma.

I don't see email going away.

On the other hand I do see Facebook going away.

zing!