Imagine a World where announcing a new issue of a newsletter would not only send a notification to all subscribers, but also update the Twitter, Facebook or Google+ pages related to that newsletter.
How would this work?
In terms of UI, Manage newsletters would include fields for Twitter, Facebook, and Google+ URLs (or whatever their respective APIs take). Probably the same message sent to Echo could be recycled for social media.
In terms of backend... if this "social media integration" is difficult to implement in the extension and/or have them deployed in Wikimedia servers, then maybe an option would be to have a tool in Labs that would somehow be subscribed to newsletters, would have access to the Newsletters details, and forward messages where appropriate?