Tbh what is really needed is optimized message passing ala the actor model. It is a leap forward and avoids a lot of problems that threads face (subtle concurrency bugs).
Yes it does avoid many problems, but it's unsuitable for other important scenarios. We need both. Message passing should be a design choice, not an excuse for a limitation in some language runtime.
The scenario I deal with most of the time is a large, read-mostly, in memory custom data structure that is accessed by multiple clients. More and more data fits into memory nowadays so that's going to be a very common scenario for many data analysis tasks in the future.
You mean CSP-style, like Alef and Limbo from Bell Labs? Have you come across PyCSP? It has multiple backends, including greenlets which are nice and lightweight. http://code.google.com/p/pycsp/
