Agree with the OP that SQL will almost assuredly still be in use for 20+ years in the future, given the simplicity and flexibility of the declarative language,

Agree with the OP that SQL will almost assuredly still be in use for 20+ years in the future, given the simplicity and flexibility of the declarative language, standardization, and as applicable to today as it was then to our big data problems. Any discussion of SQL at scale must include ClickHouse [https://clickhouse.com/docs/en/install#self-managed-install https://clickhouse.com/docs/en/install#self-managed-install], given it's broad open-source use, integrations available for Spark with JDBC [https://github.com/ClickHouse/clickhouse-jdbc/ https://github.com/ClickHouse/clickhouse-jdbc/] or the open-source Spark-ClickHouse Connector [https://github.com/housepower/spark-clickhouse-connector https://github.com/housepower/spark-clickhouse-connector], and capability to scale SQL as a network service. Disclosure: I work for ClickHouse