Afk penalty should be treated the same as entering a duel. I can see how it could be a good thing but it needs limitations.
Maybe is people were specced automatically when it was set (or if they joined after it was set) and got a message warning them about the AFK penalty. This way people who weren't already AFK would just re-enter and nobody would be caught by surprise. It would be similar to the system used when a server is set to duels.
All you have to do is when you activate AFK Penalty, it acts as if a duel has started.
Upon joining, you're automatically put in spec and OP cannot fenter you unless he turns off the Penalty, but if activated again everyone is fspeced. It's not hard if they done duel how it is.