Hey @lrynek - looks like I missed this topic originally - sorry about that!
The ES roadmap didn’t carry over to OpenSearch - and this feature wasn’t actually deprecated when OpenSearch forked and it’s not on the OpenSearch roadmap to deprecate it currently. Additionally, the ES Roadmap has no bearing on the OpenSearch roadmap since the fork. All that said: I think you don’t have to worry about it!
As a general statement, OpenSearch uses SemVer to version, so for the project to deprecate anything you would have warning of at least a minor version and it would only be removed in a major version.
Additionally, the project is community driven - so if you are using it and it’s not blocking other users, I don’t see why OpenSearch would remove it.