From the explanation, it seems to me that Raindrop might provide some of what I found missing from Google Wave. Having sat through the Google Wave Hackathon Day the problem I most had was with the user interface. The protocols and architecture behind Google Wave are elegant, but the user interface is not. Perhaps Raindrop could be a people-centric front end to Wave. After all raindrops can result in Waves. ;-)
There is a flash video explaining the Raindrop design. The first iteration of the interface design "Inflow" shows just two panels on the screen, with a conversation shown by intending of the text. The second iteration of the interface design is called an "Inflow Grid", with a rectangular table of messages.
In all of this it should be remembered that there has been considerable work by others on how to intelligently sort messages (such as by Eric McCreath and Judy Kay).