I love this. It's always nice to see PHP being implemented on new platforms (we already have it to some degree running on C++, on JVM, on .NET, now on PyPy). Sadly most of those projects don't really make it to a production-ready state :/
It's very different to use the PyPy toolchain that is to run on JVM or .NET. It does not reuse any bit of the Python VM, but uses RPython as the implementation language. You don't share bytecode, you don't share objectmodel. You share the garbage collector and you generate the JIT for your language (unlike reusing the existing one).
This is one of the most fascinating things about PyPy, and one least understood (most likely because the primary output of the PyPy interpreter generator happens to be a Python interpreter written in a static language much like Python called RPython).
I've been toying with the idea of building a little language, just for fun. The mess of building an interpreter has always kept me from it, but as I've spent some time looking at PyPy, I think I might just have a go.
I have more faith in this project, seeing that it was sponsored by Facebook. I was actually saying the other day to some programmer friends that with all the engineering effort Facebook puts into getting PHP to scale for their own system they should just take over the project, rewrite the VM and deal with future features. If anything, I think a PHP fork from Facebook has a better chance of surviving than all the other forks we've seen.
In any case, keep up the work!