After cpyext and cffi, this is the third attempt, largely driven by PyPy people, to get a C-API that people want to use.
If they succeed and keep the CPython "leaders" who ruined the development experience and social structure of CPython out of PyPy, PyPy might get interesting. If they don't keep them out, those "leaders" will merrily sink yet another project.
cffi is used to wrap c libraries. Only a masochist would use ctypes to wrap a whole library. While both are technically FFIs, it does not make sense to compare them. From a conceptual perspective, cffi was written to replace the C-API for C modules.
If they succeed and keep the CPython "leaders" who ruined the development experience and social structure of CPython out of PyPy, PyPy might get interesting. If they don't keep them out, those "leaders" will merrily sink yet another project.