I like annotations as much as the next guy but it's a complete non-starter for our business (and, I suspect, plenty of others) to add full text search to our existing apps via Hibernate Search if it means we must convert all our existing hbm.xml configurations into annotations. The regression testing alone would kill us.
The Hibernate project has always been supremely pragmatic which is why I've filed this as a bug rather than a feature request. I don't think Hibernate would have been half as popular if it didn't support things like direct SQL and reverse engineering tools. I think Search would see a big boost if it could be easily added to existing applications.
Please consider adding the needed syntax for xml mapping. At the very least an entry in the FAQ that explains the lacking is needed.