ListMediator and ProxyCollectionMediator can be registerd in the Facade without creating classes.
But if you do, you gain more flexibility in the future expansion of the application.
Actually, this is not a good practice, this is an obligation. Because PureMVC instanciate a new Command each time a Command is trigered, there must be an default constructor.
You have to provide a Subclass to ProxyCommand that will declare a default constructor.