Any thoughts ?
You might use jboss-ejb3.xml, but there are a lot of drawbacks.
There is no XDoclet support (most of developers used that to generate XML).
Also there is no support for EntityBeans which are optional in JavaEE7 spec.
From my experience most of the migration effort is EJB CMP, SLSB and SFSB migration is very simple.
If the legacy application has a short lifetime I recommend to stay with JBoss AS <6 or use EAP5 if you need support.
If the application is still alive I would migrate to EJB3 and new technology as this is better to maintain and you save the effort for migrate the XML which can be hard as well.