Sorry for the long delay but now I have finished work on this issue. I have created a PR: https://github.com/hibernate/hibernate-orm/pull/1849

After a little bit more analysis i realized that my initial approach by extending AuditProperty.function(String) would not support all possible functions. I implemented a more flexible approach. For details see the javadoc on AuditEntity.function or the provided unit tests. Lets me know if I should do any more adaptions to the code base before the PR could be accepted.