It looks like there is a strong interest for "chaining" in the PubSubHubbub protocol, as it's a topic that appeared in many other discussions. As per the spec, the subscriber is supposed to subscribe to the hub designated by the publisher in its feed. So, by default, I don't think there is any chaining possible. However, for some reason, a subscriber may decide to use another hub to gather all the updates from the designated hubs. In this example, the subscriber choses what hubs he wants to use and then expects the hub to act as a subscriber to other hubs. I believe the current spec applies pretty well to this and I do not see any significant reason why this would not work.
Is this enough for anyone who wants to do chaining?
