Currently the Magma build scans all classes to find which ones needs JPA enhancements, and then delegate to the proper enhancer. This task is really time consuming, expecially when running in developer environment where it has to be carried out at each redeploy.
It would be easier to identify entity classes and limit the scope, still not requiring the user to mantain a persistence.xml file.
The hard part will be to avoid including classes explicitly "unmanaged" by the user. That is, if the user has 10 entity beans, and explicitly writes a persistence.xml file including only 9 of those classes. Proper check during build must be placed to avoid reporting all the 10 classes.