I think taking actions
in notifications will become increasingly popular, if not the norm. Both iOS8 and Lollipop (Android L) provide a much richer set of action-in-notifications capabilities. Why force the user to open the app (even if it's a great app) if you can provide sufficient context and calls-to-action at the same time the user gets notified, and all the user has to do is click?
Note that this approach also opens up the notifications space to more than just messaging & notification-type apps. Pretty much anyone who builds a useful app can get in the game.