data: directory for data files.

This is still only a half-baked idea at this point, but I'm currently
leaning towards keeping the "<name>.data" sysconfig subdirectories in
the wheel format cross platform (and somewhat Python specific), and
adding a new "<name>.app" subdirectory in parallel.

It's important to point out that the distutils/setuptools implementation of installing setup "data_files" offers a loophole now to achieve the "app" notion (at least when installing from sdist).

When "data_files" paths are absolute, it honors them as absolute, allowing you to install anything/anywhere, if you have privileges (otoh when paths are relative, they go into the sysconfig "data" path as you would expect)

as noted, wheel installs have no such mechanism, because there's just "*.data" and it maps to sysconfig "data" in the pip wheel installer. Also note that bdist_wheel actually does the wrong thing now with absolute "data_files" paths by letting them end up relative to site-packages https://bitbucket.org/dholth/wheel/issue/92/bdist_wheel-makes-absolute-data_files)

but I agree we need something more than "data" for platform-specific data files.

Marcus