Also, I wouldn't call it inefficient. It increases the glance-and-go mentality. And as to it being redundant, they mentioned about priorities changing. Which if the priorities change, then it's already pre-setup so that when priorities change, you can adapt with no further settings changed. What's redundant about that?
To me if there's sound notifications that are not important enough for the user to pick up the phone it's the very definition of inefficient. Even if the priorities change, then the redundancy is just shifted around. If the application A is suddenly important and application B is not anymore, then the sound notification for application B has become redundant.
I guess my argument is more about this point. Since there's lock screen notifications and Live Tiles that will ensure that the user will get notifications even from low priority applications next time they pick up the phone, why should there be a sound notification for them at all? Instead of having a system where user has to define notification sounds manually and adapt to their priority, I'd prefer an intelligent system where the device will figure that out for me.
Play that one distinct, familiar notification sound that I easily recognize from anywhere and play that only when it's something that I want to be immediately aware of. Off the top of my head:
Example situation:
I get a phone call and do not answer it.
Phone AI analysis of the situation:
Location data kept changing for the duration of the call and the proximity sensor data did not change = I was walking with my phone in my pocket and did not hear the call. That person is also attending the same Facebook event tomorrow as you are and you have an active Messaging history with her.
Notification adjustments:
If the same person calls again, check sensor data if you're still walking and if you are, increase ringer volume by 50%.
Enable notification sounds for that person even in the social networks you've muted (Twitter sound notifications were muted, now active if a DM comes from her) for the rest of the day or until you've had some interaction with her.
This sort of notifications AI could work with anything. WhatsApp sounds from group conversations would be muted except when the AI detects that you were mentioned. No personal email box sound notifications during working hours and other way around. Endomondo running and accelerometer shows active moment, mute all notification sounds from all social networks. etc.