Having said that, I would really love to see this be supported by ST. I posted a feature request on the old discussion board a while ago, but that didn't gain any traction. I don't think people see the value in it, but it's probably my fault for not "selling" it the right way. I think it would be the perfect pattern for SmartApps to publish subscribed to events via the API endpoint. It would cut down on polling requests from third party clients, and could maybe help take some load off of the ST cloud.
Architecturally, there exists a two-way communication between the Dashing backend, and the SmartApp endpoint, in my case. The SmartApp posts requests to the Dashing backend, when events occur, and when the client changes the state of a device (e.g. light switch), the communication flows the other way, with the Dashing backend posting a request to the SmartApp endpoint. Does that make sense?
If you are thinking about creating a backend for your own dashboard, here is a great tutorial on how to implement Server Sent Event streams on the backend, and EventSource on the fronted. It's actually pretty easy!