Unfortunately this could lead to a new method of trolling you - if they know they are on your blocklist and not being rendered all they have to do is follow you around and interact with the world around you. (I.e. kill the mobs you are going after). From your perspective the enemies will die but you won't be able to see who's doing it (it will look like the bots that use the clipping method to target/kill mobs from below the ground). Granted some trolls do this anyway (there was a lvl 80 ninja who thought it was funny to one-shot kill the mobs I was trying to learn BLU spells off a while back) but it would make it far harder if you can't see them.

Plus as you say, what's to stop them going off and creating a new character to troll you with.