Mechanism against killing grey lvl players should be these grey lvl players asking for a help from their faction, and having a lot of active pvp players in this server means it will be easy to find a retribution team that will come and punish the gankers, which certainly were, are and will be in WoW. The game is called Warcraft for f**ks sake - creating limits to kill another faction is weird.
Please do not do such things to create additional shenanigans/exploits and limit the fun.
If there are people who are not happy being killed - they can go play Hello Kitty Party Land.