Today Hibernate does not actually "understand" even what an EXTENDED PC is... WF/Jipijapa handles that and converts it into Hibernate's terms. PersistenceContextType really boils down to 2 things for Hibernate...
1) what is the Session FlushMode
2) should I automatically close the Session after transaction completion

An EXTENDED PC, to Hibernate, would behave like:

1. FlushMode#MANUAL
2. false (do not automatically close)

I think the most appropriate solution is to simply add a FlushMode check in AbstractSaveEventListener#performSaveOrReplicate when deciding shouldDelayIdentityInserts. Specifically, any FlushMode "less than" AUTO should delay the IDENTITY inserts if possible. Something like:

boolean shouldDelayIdentityInserts = !requiresImmediateIdAccess && ( !inTxn || source.getHibernateFlushMode().lessThan( AUTO ) );