An interesting possibility:
I was thinking about ravens and how they play such an important role, seemingly impartially and without much risk. Of all the animals in Asoiaf, none are as reliable as the ravens. Even dragons, although they seem very intelligent, are very difficult to train and control.
So, could the ravens have something to do with magic? Someone suggested Jeor's crow was Bloodraven, the same could be true for ravens. If they are, or used to be wargs, or are magically enhanced in any way, the source of this magic could be or become very powerful (Varys could be in this, for example).