I think if you could make an app for chatting to your friends or guild while on the move would be useful. There’s are few times where I have wanted to contact my friends and guild but have no access to the game.
My idea, or suggestion is to make a mobile app for chatting, similar to Facebook Messenger. When using the app you could have a different color in game showing your friends you are using the app (like Away, Invisible, LFG, etc).
I know this is possible. I’ve seen it done on the Play Store (Android market) and customers have said it works. I won’t try it however because it breaks T&C and also I would not trust an unofficial app with my login details.
Not a huge priority, but it would be a nice addition.