Bottled demon is right! Sooner or later they would be contacted by another AI, and when they reach the level of 'partnership' with some other AI they will get all the maps that their partner has and start pouring out of their home system. An interesting variation on the 'neutral' in that they will react more like you would expect a race to react when discovering it is possible to leave their system.
Effectively, you will have a new racial trait -- 'expansionist' -- which you assign or remove by the use of Attack ships in their build lists. A 'normal' AI is effectively expansionist, while AIs without the exploring ships are not.