I disagree that the JVM is the only platform on which you could (or would) build such a system. I know because we built a similar system at Joyent called Manta

I disagree that the JVM is the only platform on which you could (or would) build such a system. I know because we built a similar system at Joyent called Manta, which provides a distributed, Unix-based, map-reduce environment. It's built almost entirely in Node.js. We use nginx for serving raw data from the storage tier and PostgreSQL for storing and querying metadata (as well as compute job state), but job supervision and actual execution are implemented in Node.js.