I have just packaged pypy, another Python implementation. It is python-2.7 compatible, so should work with the 'noarch' python packages for python 2.7 (just ask pypy to look into /usr/share/python2.7/site-packages too). It would work if the *.py files were provided and not only the py2.7 pyc files..
IMHO it is another reason to start including *.py files in the packages, making 'pypy-*' with pypy-compiled files for every 'python-*' package, just for the few who would ever use pypy doesn't make much sense to me.
And the Python 3.2 __pycache__ directory starts to make more sense when another python implementation comes to play…
We could have one /usr/share/python/site-packages, which contents could be linked to compatible python implementation's site-packages dir (like it works for browser plugins). Some packages could even work for both python2 and python3, others just for python2 and pypy, etc.
The __pycache__ could be populated by the %post scripts. python2.7 and pypy could be patched to use that as 3.2 does, but we could also keep python2.7 *.py[co] files the old way.