So I guess the specific issue that grandparent raised was if multiple users wanted to edit the same record. So even if the queue is sharded on some primary key, then for each partition, either a) you only have one machine ingesting and thus a SPOF, or b) you ingest data using multiple machines, which means you need consensus/conflict resolution somewhere, right?

That doesn't answer my question. If you're appending to the end of a table, regardless of system you still need one machine somewhere to ingest new records for the same primary key, right?