When a notification of a task due is visible in Android, add the feature of expanding the notification, to show a text that says “Mark as complete”, in order to mark a task complete from the notification without having to open the task.
It is indeed a useful feature, but unfortunately not as simple as it seems. One complication is that the task to which the notification refers to may not yet exist (if it has to repeat today, but the app was not open today). To provide some context, essentially we would need to load all the data, run auto-sync, run the scheduler to create any still missing repeated items, then we can actually mark the notification item as completed and run sync again to push changes. This is why this feature is not yet implemented.