Very cool project. Like others say, it can be a pain to debug generated code in opal, clojure, elixir etc. But that's also true of the code generated by the C compiler. This is a chicken-and-egg thing. Either consumer hardware gets so fast that it's feasible to implement the language vm's in javascript or browsers will support other mechanisms for implementing them. But only when these projects are used by many people, which will happen when the code is easy to debug.