I think something needs to be cleared up. Third-party apps do not get free reign over notification interactions, it’s very different to Android. As it stands today, third-party apps can only add two buttons to notification banners (as shown here). These buttons can trigger actions, without the app having to be foregrounded, but anything more fancy than clicking a button is off-limits. You don’t have the same level of flexibility as with Today widgets or share extensions, for instance.
The quick-reply feature is only supported for Apple’s Messages app. This functionality is not available to third-party apps. No one else but Apple can declare custom UI for their notifications; third-parties get two buttons and that’s it. This severely limits the amount of “stuff we haven’t imagined yet” that is actually possible with the current system.