I cannot imagine why would one write (ALL, !root) policy -- this seems like a security hole waiting to happen. There are many system users, and I would not be surprised if some of them can be escalated to root.
Some people do try en enumerate all bad conditions, I have seen this with my own eyes. cp /bin/bash myehell, sudo meshell. I have never seen anyone try to enumerate the user part. I'll be waiting with popcorn.