Hey @sedouard, I think this looks pretty good - there's a bunch of UI work left to do, tests aren't there yet, bulk & promise notifications aren't implemented yet - but performance right now is awesome.
Plus, I did use Ember.Object, giving us all the benefits of observers and properties 🚀
First Notifications Draft
Basic Styling for Notifications
Implement "Remove Notification"
This looks pretty good to me now, I added a few things. I'm bold enough to probably merge this as it is and fix all troubles you have on top of it.