I am designing a 3D FPS mobile game using Unity3D. The game will be released with an initial set of characters. I want to periodically release new sets of characters. At release, I won't yet know how the characters will look or how they'll behave.
An example: The game is first released with a set of domestic animals. The player can feed them, pet them, etc. Six months after release a set of birds are released. These birds fly which the animals did not; they like different food that other animals did not. Another two months later release a set of wild animals that can be hunted down. How can I release this set of birds and animals with all attributes and animations as a package?
The intent is to keep the animation team on a separate schedule from the game development team so the animation team can independently test and release packages to keep players involved.
How can this be done with Unity3D?