I love the continuous queries over append-only datasets and it's great that Kafka added support for it.

It looks like there is one main contributor (https://github.com/confluentinc/ksql/graphs/contributors) though, it seems that the other contributors either wrote the documentation or helped for the packaging. Not a great sign considering how big this project is (there are competitors which only do this such Pipelinedb), hopefully you can create a team just for KSQL.