This is a proposal for a generic version of PubSubHubbub which 

1- Supports the use of OAuth 2.0 for authenticating the subscriber and publisher.
2- Moves discovery of the hub to the HTTP layer by making it an HTTP Header
-- Leaves backwards compatibility for existing discovery mechanism.
3- Supports data in any arbitrary format including JSON
4- Supports more synchronization changes than those which can be supported with Atom and POST
-- Includes PUT for replacing a resource and DELETE for asking that the resource gets deleted
-- Also includes the ability to specify different end points which receive DELETE notifications and PUT notifications

Motivation: http://montrics.blogspot.com/2010/05/facebooks-realtime-updates-use-cases.html