7
This would be a very handy feature; my company has looked at adding it too. We don't have an urgent need at the moment though. We have spec'd out a UI addition that would let you manage permissions on multiple groups at once, which would help deal with lots of non-hierarchical groups better. You can read that spec here (attached to this sourceforge posting):
http://sourceforge.net/tracker/?func=detail&aid=1017424&group_id=41586&atid=430843
As far as groups inheriting settings from other groups, the easiest way I have thought of for doing this would simply be to allow groups to have other groups as well as users as members. This would essentially eliminate the need to make people members of lots and lots of groups, you would only make people members of playersHalfLife, playersDOOM, etc, and then those groups themselves would be members of playersFPS, and so all the permissions attached to playersFPS would apply to the users who are members of playersHalfLife and playersDOOM without you having to manage complicated membership settings of multiple users in multiple groups.
In order to make that happen, you would have to modify a lot of the core libraries to do with checking permissions and group membership. It would be a complicated change, for sure.
No matter how you set about to change this, it would be complicated.
--Julian