The ability to disable global chat ("disableGlobalChat"), enable local chat ("enableLocalChat") and specify it's range ("localChatRange") in the server-side config.
These chats will then appear on clients just as IRC channels would and can be switched to. Also, "enableTeamChat", using Minecraft's scoreboard team system.

Not so sure about this anymore. Might not fit into the whole "IRC" thingy. Put on hold until it's actually requested by someone.