Hibernate ORM 6.0 alpha 1 was recently released (in December 2018). Let's introduce a org.springframework.orm.hibernate6 support package in the Spring Framework 5.2 timeframe, in parallel to our existing Hibernate ORM 5.x support.
At this point, it looks like Hibernate ORM 6.0 won't be final in time for our 5.2 GA timeframe in June. While we're going to make sure that Spring's JPA support works fine against Hibernate ORM 6.0 pre-releases, a dedicated org.springframework.orm.hibernate6 package is probably better off in our next feature release.
On review, HibernateTemplate does not seem feasible to sustain anymore against Hibernate 6.0 since plenty of underlying API has changed or even been removed. We meant to phase out HibernateTemplate before, so this seems to be the definitive time for it. We can keep the Hibernate 5.x variant of HibernateTemplate around but won't introduce a dedicated 6.0 variant.
For all common purposes, our JPA support seems to be compatible with Hibernate 6.0 since #28007. From that perspective, there isn't much need for dedicated support for native Hibernate APIs from Spring's side. That said, let's keep this general support ticket open for the time being, to be revisited towards Spring Framework 6.0 GA for a final decision.