(Contributor to skulpt and pypy.js here)

That is a difficult question to ask and I think the original developer of pypy.js Ryan Kelly is most suited to answer it. There are some people that have tried feeding the asm.js from pypy.js to the asm.js -> wasm compiler.

Which with a lot of fiddling may work for the non-jitted version. But if you want all the pypy speed you'll want to jit wasm to the browser.

I would love to know if you can do synchronous calls in wasm.