As mentioned in the PR:

I do think a better long-term solution is to introduce an EnversFlushEventListener that extends the existing FlushEventListener and will control the flushing process inside the Envers module. This avoids the need to expose an internal class externally.

More importantly however, is it provides a single, consistent user experience to where flushing happens simply by calling flush() on a Session or EntityManager. Envers simply handles it automatically as it should.