Hopefully this will be a more useful spec.
Thanks for the proposal, but it is not really a spec. You’re suggesting name and syntax for a new field, but you don’t describe what it means and what it is used for. From what I understand, the goal is similar to build dependencies and optional dependencies in systems like Debian’s dpkg; for the build dependencies, there were multiple threads about adding Setup-Requires-Dist (like setuptools’ setup_requires) and Test-Requires-Dist (like tests_require, or whatever the spelling is—I always get it wrong :), for which we were near to agreement. See https://groups.google.com/forum/?fromgroups#!searchin/the-fellowship-of-the-... and https://groups.google.com/forum/?fromgroups#!searchin/the-fellowship-of-the-...
This begs for parenthesis in environment markers, something that is easy to do by compiling markers to Python functions using the ast as `markerlib` does.
distutils2 supports Python 2.5, which has _ast but not ast IIRC. If you have other suggestions for improvements like this please open bug reports though! Feedback and patches are welcome.