Wave Protocol Prototype Source Code
code.google.com
code.google.com
Perhaps someday.
I'm interested enough in Wave to consider reverse-engineering that portion. I think there are some once-in-a-lifetime opportunities here...
And yep, some people can't wait so here is a server implementation (Python/Django):
"Yes! The plan is to release a reference implementation of the client, as well as the server. "
While Wave is a good idea, and the hype is justified for a closed system, implementing it on your own system requires a deep, DEEP knowledge of Javascript.