Description of problem: PAM need to gain support for /usr/lib/pam.d/ which would contain built-in defaults or static vendor-supplied configuration files, for pam to support booting with empty /etc . Administrators should be able to override and or add additional local configuration files in /etc You can see a bit more about this here [1] 1. http://0pointer.net/blog/revisiting-how-we-put-together-linux-systems.html
The support for the /usr/lib/pam.d is in rawhide. The migration of the configuration files there is another thing and I am not currently persuaded it is a right thing to do just now.
What's the issues you have against it?
For example there is no support for individual module configuration files in /usr/lib so you would still have things in /etc/security.