I don't know much about the project but I have a lot of experience with asm.js. Using asm.js has many drawbacks and should only be used if the tradeoffs are acceptable. Some of the large issues:

- A bad debugging experience (no segfaults on null, local variables are numbers instead of strings or objects, function pointer calls are super confusing)

- Much more difficult to interoperate with external JavaScript libraries

- Massive code bloat (you have to reinvent everything like arrays, strings, maps, regexes, memory management, etc. instead of just using the browser's built-in implementations)

PyPyJs does that. It's complete, but loads very slowly. In practice that's a problem not so easy overcome. And debugging and JS interop is a problem.