Work has been initiated as part of HSEARCH-2260 In Progress , but some major changes may be needed, so this will have to be part of a major release.

Work in progress available here: https://github.com/yrodiere/hibernate-search/tree/HSEARCH-2260-clitool

The main issue was that such a tool should not have to connect to an Elasticsearch instance: we just want it to export the schema based on a configuration and a set of jars. Yet HSearch's metamodel creation and index manager creation/startup seem intertwined, and we cannot execute one without the other. So in order for the CLI tool to exist, we need to bring some changes to HSearch's startup process.
See there for more details about the issue: https://hibernate.atlassian.net/browse/HSEARCH-2260?focusedCommentId=84220&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-84220