Off topic, but you might consider flagging some bugs as good starter bugs for joining the project. You have great technology but it's a challenge diving in to it, even with the docs.
Some more info/caveats of Cython's cpyext support can be found here:
It's possible to write a Cython backend that would generate cffi bindings instead of C, but the work has not been done yet, so it's a bit unclear when it'll happen. Would be a good summer of code project for example.