lanceball
As for coding Java on Nodyn, well, yes you can. That's kind of the point in some ways. You can write Java, package it as a jar and access this from Nodyn. Nodyn itself does this for the Buffer implementation.
Yes, vert.x already supports JS (I maintain the mod-lang-js, mod-lang-rhino and mod-lang-dynjs language modules for vert.x). The idea behind Nodyn is to provide drop-in Node.js compatibility in the Vert.x environment.
Nodyn is not yet complete, though I'd like to have a release in the next month that is capable of running express.js apps. It is slower than Node.js, but of course I'd like that to change; and with the JVM underneath, beating Node.js on performance is possible.
Nodyn is built on top of Vert.x (http://vertx.io) an asynchronous polyglot platform which excels on the Techempower benchmarks. The javascript runtime is DynJS - a new JS runtime for the JVM which is independent of Oracle. Though it's admittedly slower than Nashorn at the moment, we hope for that to change.