Fedora already publishes all events as JMS messages. The most natural way to hook fedora is thus to set up a jms message listener.
We already have code for this
Why no worky
We have a bad track record with JMS, with frequent crashes and reboots in the Bitrepository system.
JMS do not have a natural rebuild-strategy. It would be nice if the update tracker could get updates and rebuild from the same source