Thanks for your response. It is a good thought process.
I had a similar discussion on my LinkedIn post. I will try my best to answer your question too.
This approach is a guideline to start building facade service. It can be extended/tailored based on project needs. For example, you can facade service at module level or you can detect when module is unloaded (by handling some Angular life cycle events or firing custom events).
With Angular 6 version, they have changed how you can provide service to module. Now service will specify in which module it shall get provided rather than module specifying services in providers section.
I will write another blog explaining this new approach soon.