Despite the Rhino-related name, Nashorn (the German word for rhinoceros) is an entirely new code-base that makes extensive use of Java 7's InvokeDynamic byte code instruction. The resulting implementation is both smaller and considerably faster than Rhino making it more suitable to run on embedded/mobile devices; it runs on both the Beagle Board and Raspberry Pi for example.
I was blown away that first of all everything just worked - I never ran into a correctness bug with the Nashorn stuff. And on the performance side on the most challenging tests it was more than 20 times faster than Rhino.
A blog has been created to go with the Nashorn proposal. Voting has now begun and runs until 6 December. With Nashorn already 100% compliant with ECMA-262, initial work within the OpenJDK project would concentrate on performance and hardening the platform for general use. Potential OpenJDK collaborators include Twitter, IBM and Red Hat.