It would be really cool (possible unrealistic though) if an IRC (or some other form of chat) client could be built into the game interface itself. Would be a nice option to be able to chat about your game while playing, ask for advice, etc, without the disjoint experience of having to play in a window or constantly alt-tab.
Depending on how things are set up, I could see this either being pretty easy or incredibly hard, though - (Although if it could be set up as the backend to whatever communications system was set up for normal multiplayer it might not be that bad - especially if there's some open source IRC code that could be used under a commercial-friendly license)