With "distutils users" I'm referring to people that are told to run
"python setup.py install". Changed affecting the way this line behaves
need to be carefully considered.

OTOH, when upgrading a package to a new Python version (and distutils
version), package authors will have to modify their packages anyway, so
it is well possible to ask them to use Unicode strings for meta-information.

Supporting pre-2.6 Python version is also not much of a problem, since
authors could setup the strings in question to be either Unicode or
8-bit strings depending on the Python version.

This change would be really minor (compared to e.g the Py_ssize_t change
;-).

That said, I don't think it's a good idea to make package data more
complicated by allowing multiple encodings. The meta-data file should
have a fixed pre-defined encoding, preferrably UTF-8.