While many interfaces are “just” defined by the name alone (because the name implicitly defines the interface type) some interfaces are richer: they can have multiple plugs or slots with different names (but same interface type), and with different attributes. The prime example is content interface which can be composed in almost arbitrary ways. The dbus interface is also like that, it has attributes that define the semantic and also the permissions granted when connected. The media-hub interface feels like a remnant of the Unity 8 work and I don’t think you will find much use for it in practice.
