Complex ViewModels can contain automated navigation such that, upon an event being triggered, automatic popping of the back stack can occur. Adding a constructor argument to ensure a PopBackStack instance's execute method is successfully executed once, adding the ability to elect to do so would help mitigate potential multi-submissons resulting in multiple popping of the back stack.
As the RequestDriver wraps the Request with an id to ensure single execution of each submission, this would enable single execution of each request.