Sometimes you just want to verify your code with fellow devs or just want to ask a question. 
How nice would it be to tag developers by an @[NAME] in a comment (reminder) who also have access to a app/module.

In this way you can also do code-/peerreviews much easier and even ask questions without killing your focus/flow.
The tagged developer gets a notification (Service Studio and/or Mail) and can respond when it suits him/her.

Next step would be to respond to a comment (new idea?!) with a follow up.