I think another good way of controlling the chat to some degree is that players can right click the name of someone who typed a message into world chat and chose to recieve coords to his position. (Would scare most people from typing in chat randomly when they feel like if the game has open pvp).
Troll 1: <in global chat> I think you all suck
Respondant: <select coordinate location>
Respondant: <Travels to location>
Troll 1: <In local chat> Sucked in loser!
Troll's 2 - 10 <Hidden in bushes> giggle..attack!
One possible outcome which makes the tool as a form of discipline probably a better tool for trolls.
It is difficult to control world chat, control it too much and players will move to alternative forms of chat. One way you might try is an ingame "pay as you speak" in keeping with the way telegraph/telegram systems work. Each word costs a coin -- the more you speak the more you spend your ingame currency.