The idea has come up before and though it sounds good in theory, it just doesn't make sense for our server. If we are going to have more staff, they might as well go through the whole process and be full GMs because they are fully accountable for their actions and command more respect for their position.
What I mean is, if we have moderators and they started enforcing the rules that they can, then players will likely start claiming they were abused by the moderator or they were abusing their power. In the meantime, the GMs would have to go back and investigate what actually happened to make sure no abuse was going on. It would create more work for GMs and possibly more liability for the Admins in regards to server rule enforcement. So that is why it makes more sense to me, to make a GM over some moderator position with limited powers.
I will pass this along to the other staff to read and consider, but I highly doubt you will ever see a moderator position any time soon. I also believe that there will always be gaps in GM coverage no matter what so this thing is going to happen. Right now the server may have player spikes during times when its normally lower because all the kids are out of school for summer.