C/C++ and Python constitute a solid basis for many mature scientific computing platforms. It's futile to try and redo the world of high performance computing inside the browser, it's like squeezing an elephant into a mouse hole. Having said that, some computational capabilities in the browser would still be handy. Afterall, if something runs in the browser, you can show it to anyone.
Another application of Numscrypt is to use it as a platform to try out technologies like asm.js, simd.js and GPGPU for the most time-critical parts of the code. Forking and experimentation encouraged!!