This is awesome. The sandboxing architecture (clusters, ELB, controllers, Docker, etc) is surprisingly similar to the one I implemented for <a href="http://repl.it" rel="nofollow">http://repl.it</a>
It's made simpler since I have network access disabled on the docker containers, but check it out, it can run Node as well as host other languages: <a href="http://repl.it/languages/nodejs" rel="nofollow">http://repl.it/languages/nodejs</a>