Is anyone using the druid-kubernetes-extensions in production? Its still labelled experimental, although there's an issue to take it out of that status (from 2022 😬). It doesn't look like its under active development based on the history.

Yes, it is widely adopted now, and is fairly stable too, with several improvements made recently such as https://github.com/apache/druid/pull/18599. It should move out of experimental status soon, perhaps the next Apache Druid release.