I feel in the admin panel the owner/founder/head admin should be able to pick weather the user receiving the warning can see who sent it or not for staff safety. I also feel that when the admin picks if they user getting the warning can not see what staff member sent it there should be a box they fill in a username to a staff member or a made bot account that sends out warnings.
I also feel that the subject for staff only should be in color (admin choice) so any staff sends warnings, reply's, message's there subject will be in color.
This sounds like a great idea. I'd really like to see more flexibility with the warning and permissions system. I'd really like to be able to establish a class system within my management team and limit the types of warnings each level can issue.
Not just custom warning but I would like to be able to define exactly what types of warnings different levels of moderators can issue as well. You may want to read the Moderator tools thread to get a greater understanding.