I always tried to keep Hibernate Search as agnostic as pragmatically possible wrt Lucene, so a Solr integration can be envisioned.
If someone wants to explore the idea, contact me.
That being said, your justification for using Solr is not good enough :)
You can index a data even if it has not been added or updated to the DB though Hibernate
http://www.hibernate.org/hib_docs/search/reference/en/html_single/#search-batchindex
Also the idea of updating an index based on a timestamp or a version number crossed my mind, I might want to integrate such a feature to Hibernate Search in the future.