According to announcement by Oracle, OracleJDK will be published only to users who pay and subscribe MOS. Though OpenJDK is still available, it seems to have no LTS release. In other words, users who want to maintain Elasticsearch service in an online production service may have to keep upgrading their Java version every 6 months as a new Java version is released to keep the runtime up-to-date.
For my own opinion, a more reliable solution is to migrate runtime environment from something hosted by Oracle, such as OracleJDK and OpenJDK, to something hosted by other open source foundation, such as OpenJ9 that is hosted by eclipse. So is it possible that Elastcisearch may consider to support OpenJ9 in the future?
I suppose 'OpenJDK 9' is different from 'OpenJ9'? OpenJ9 is another Java runtime based on OpenJDK and maintained by eclipse foundation. https://www.eclipse.org/openj9/
Though I'm not sure in the following case, the mentioned 'IBM J9 VM' is the same thing from 'OpenJ9' or not, but at least they should work pretty much like each other since OpenJ9 is originally donated by IBM. And in the matrix, IBM JVM is still unable to run Elasticsearch.