Hmm... too bad, it sure ould have been nice.
But an addon can write to a textfile in the WoW-folder... It doesn't happen to be possible to have a program that catch the input to a file, redirect it to an IRC-client somehow... and the outher way around, adds what people say in the IRC-channel to an file that is checked by the addon every five second or so, and displayed to the player...
I may not be that skilled in programing (yet), but at least I try to keep ideas comming :P