Type: New Feature
CDI observers may be registered as JTA synchronization callbacks (same applies to Stateful Session Beans). Nevertheless it is currently not clearly specified which JTA interactions are legal within those callback methods. The current EJB spec contains a few hints, however I believe those clarifications should be part of the JTA spec.
In both cases - CDI observers and Stateful Session Beans - it is quite easy to execute transactional aware code within those callbacks. This includes interaction with an currently active transaction but also suspending/resuming a transaction in order to implement requires new semantics.