I imagine things like libdir, prefix, datadir, docdir and other things
copied from autoconf. Where the defaults would be something like:

prefix = sys.prefix
libdir = sys.prefix/lib/pythonX.Y/site-packages/pkgname
datadir = sys.prefix/share/mypackage
docdir = sys.prefix/share/doc/mypackage

I wouldn't want to use those. What goes in libdir, what goes in datadir? I don't know, and frankly the distinctions start getting really arbitrary.

I would rather see something like pkg_resources existing API, where there is some file that maps out how the local names of files (where they'd be in a checkout) map to their installed location, then the pkg_resources code could finds the real location of the file.