We're actively following the work of Trevor, Moxie, and all the great folks at Open WhisperSystems. Some of their work is cited and analyzed in the paper that's on the site. Of course I'd love to use and keep up with the best ideas, whatever they happen to be, and so one of the design goals of okTurtles is to be somewhat protocol-agnostic, so that it's easy to incorporate better ideas as they come along, while maintaining backwards compatibility. At the moment, TextSecure's example of async-OTR, with their modifications to make the protocol simpler (3 DHE, and the ratcheting you cite), seem quite appealing, and unless we find something better, we'll probably use that (with the exception that we won't be relying on a single centralized server).