Introduce org.springframework.orm.hibernate4 packaging, and cut a clean implementation against Hibernate 4 APIs and SPIs. This is both desirable after years of Hibernate 3.2+ support as well as necessary given certain removals (such as AnnotationConfiguration) in the 4.x line.
Eliminate AnnotationSessionFactoryBuilder and AnnotationSessionFactoryBean in the 4.x line in favor of a SessionFactoryBuilder / LocalSessionFactoryBean that work against the unified org.hibernate.cfg.Configuration; consider support for Hibernate 4 Services (http://bit.ly/gnUAUI)
Eliminate HibernateTemplate and friends (e.g. HibernateCallback in favor of Spring's more modern 'Native Hibernate DAO' approach which has been used to good effect for quite a while.
org.springframework.orm.hibernate3 will remain, though possibly as a separate module (jar) from .orm.hibernate4 for dependency reasons.