It would be interesting to see if this could make it in Python 3.2 (It's supposed to include the Unladen Swallow stuff, so might as well take more awesomeness from Google.)
Probably, but python-core has no interest in maintaining multiple regular expression implementations: http://mail.python.org/pipermail/python-dev/2010-July/101606... (this thread starts talking about regex, which is a backwards compatible enhancement to re, but also covers re2)
Yes. That's precisely what pyre2 is doing. It's trying re2, and if it fails because it doesn't support the features, it tries the python re. Since compilation happens rarely, this is fast.
Like the libxml module which uses Cython, the compiled CPP module is distributed along with it, so you don't actually need Cython to install it or compile it. But you would need Cython to do any development on it.
It would be interesting to see if this could make it in Python 3.2 (It's supposed to include the Unladen Swallow stuff, so might as well take more awesomeness from Google.)