This project idea is no longer relevant
GStreamer uses Liboil for making signal processing code faster using SIMD CPU extentions. One of the limitations of liboil is that it has fixed (although expandable) functionality, i.e., if the function you need isn't in liboil, it has to be added, and then SIMD code written on various platforms. A related limitation is that many applications require combining many simple operations into a complex, configurable operations, and proper optimization depends on the exact configuration.
One of the ways to get around these is to move liboil in the direction of compiling/assembling a simple signal processing language at runtime into fast code that is targetted for the current processor. An example of how this might work is OpenGL shading language compiled at runtime into code that runs on a GPU. There are of course existing JIT compliers, but none targetted specifically for SIMD. (Or maybe there is, and we just don't know about it.)
The project would be to either convert an existing JIT compiler to create SIMD code, or write a new one.