This sounds like an issue with one of these (but both needs to work):
- gksu should work (seems like it works now?)
- we should not require to type password to shutdown/reboot computer, something missing in /etc/sudoers.d/ ?
About pam.d: I was more like thinking to use a massive "sed -i" to /etc to replace the pam_systemd.so to pam_elogind.so in case of openrc switch 
, maybe as:
sed -i '/^session.*pam_/s/pam_systemd.so/pam_elogind.so/g' /etc/pam.d/*
about the rest: ok, what about replacing the systemd (not needed anymore) as mentioned before, fixes all issues like freezing and others?
Let's keep a list of TODO's:
gksu should work (it is used by many applications, not only shutdown)
elive-pm should work on openrc installs
lightdm should shutdown & reboot
e16 & e26+ should work too (what they trigger exactly?)
fix the pamd files to use pam_elogind.so instead of pam_systemd.so