rkoz

DNS maybe good for lightweight service discovery, people have been doing it for ages. However I wont waste anytime trying to dress it up as an answer for real world config management problems (distributed, hierarchical, model-agnostic, consistent .."stuff")

Care to explain how DNS alone can do distributed config management?

Not really - it's all about contextual actions in the Inbox. That said, Gadgets have been available in GMail and I know of no reason why one couldn't pretty much implement the same action without Google's blessing. A data format spec is a natural next step for Gmail gadgets. Microsoft also has had support for mail apps in Outlook 2013 where you can specify activation rules for gadgets/apps to show up.

The usual approach is to track acks or callbacks driven via user actions on the server-side. Adding a "guaranteed delivery" QoS will involve queuing, waiting and retrying on non-ack timers - and do so without abusing users' trust in your app.