Yes, this has been suggested before. So be quiet, i know.
The Private Chat Box (PCB) is a special chat that you can invite knights in to have a multi-knight private chat.
Commands:
/invite (player): send an invite to join the PCB
/kick (player): kick a player from the PCB
/quit: end PCB
Also there should be an option by right-clicking a player.
You can toggle between the Public chat and PCB. There are notifications when someone posts in the PCB.
Or at least divide chat to diffrent tabs so you dont see all Guild/Trade/Zone/General + Tells in one windows but you can switch between Trade tab, general/zone tab,guild tab or tell tab (or even you have a tab for every diffrent person who used tell). Also you should make able to expand chat window, it takes just 2 long trade offers to scroll all chat down and you have to constantly click click click little arrow do go backto place where someone said something to you but it got flushed away .
Would be VERY handy