Not sure if permissions already has something like this, but I'd like to see a simple command allowing you to toggle a groups permissions on/off. This way when a Moderator is playing normally, they can't accidentally do something they shouldn't be able to as a normal player, and they will only have Moderator permissions when they intend to use them. For example...
Moderator group has inheritance Default.
Bob is a member of Moderator group
Bob types /Moderator off
Bob now only has permissions in the default category, because he's turned off any permissions the Moderator group has
Bob needs his moderator permissions, so he types /Moderator on