Are the docs at https://datahubproject.io/docs/architecture/metadata-serving/ up-to-date? I read in recent changelogs that Neo4j is not longer required. I was wondering if kafka stream here is required or not.

Kafka MAE stream will be used to populate both ElasticSearch and Neo4J. Without it you'll have no search.

Yes it’s now possible to use ElasticSearch for graph queries instead of Neo4j, but we do still have the dependency on Kafka