As we have re-implemented all the connection logic, the existing driver needs to be refactored to use the new implementation.

Backwards compatibility will be important, but we will not sacrifice maintainability. For instance, MongoConnection is public, but it is highly unlikely anyone is using it. In this case, it will probably get deleted. However, MongoServer and MongoServerInstance are public and we know of a number of people utilizing them and therefore we will reimplement MongoServer and MongoServerInstance by wrapping the core concepts (ICluster and IServer respectively).