The thing I've been working on over the summer, which is soon to be released, is notifications of two types. One is old fashioned email and one is notifications send to your computer desktop or android device. At first I'm going to be testing out the new notifications with quiz comments, so when someone comments on your quiz or replies to your comment, you'd get a notification.
After the initial test, I'm going to add a page for changing account settings (including email address), which will have a configuration section for notifications. This example shows some mock notification types that may or may not be added:
The "achievements" don't actually exist yet, but it would be a cool feature.