Actually, RapGenius is the realized, "worse is better" version of Xanadu. It takes the simple idea of annotated hypertext and runs with it, and doesn't bother with all this unusual things like panning, backlinks, excerpts, and so on. That's why RapGenius is successful, and Xanadu is still vaporware.

OTOH, I don't think this is even supposed to come out. It's rather a demonstration of some pretty interesting, advanced (and thus also failable) ideas. It reminds me a lot of Jef Raskin's "Humane Interface" ideas.