I used to be extremely into Dataflow/Apache Beam and literally had the paper printed on my desk AND the book. I agree they got Event time versus processing time and Never rely on completeness right, and I love they go deeper into why that was just a hard thing to accept. My head still hurts thinking about unbounded stream triggers and I'm happy we got around to a table-centric model. I still think taking some ideas from Spanner, databases as message bus or consistency information per row, basically in-database CQRS would have been nice, though. Great paper.