I think that a function as the foundation of vassal civilizations should already exist.
A simple example:
You are France and you have territory in North America; you are at war with the UK and all its troops are in Europe; Some American civilization declares war on you when all its troops are on another continent. It is an unnecessary loss of territory when a function could be implemented to found a vassal state to serve as a cushion and to have no relations with nearby enemies.
As an example: the French would found Louisiana to have a vassal and avoid a war. It would only take