So yes, cPickle/pickle, cStringIO/StringIO, heapq, etc. are all examples of the approach. One could choose to write the pure Python version first, profile the code, and only write extension code for the hot spots, but obviously that typically doesn't happen.

As for who maintains it, that's python-dev, just like every other module that is structured like this. When the stdlib gets more of a clear separation from CPython I suspect the other VM maintainers will contribute more.

As for PyPy not specifically needing this, that still doesn't solve the problem that Jython and IronPython have with extension code or any other future VM that doesn't try to come up with a solution for extensions.