The cross-region replication I’ve seen for S3 (including the link you’ve provided) is fundamentally different from a dual-region GCS bucket. AWS is providing a way to automatically copy objects between distinct buckets, while GCS is providing a single bucket that spans multiple regions.

It’s much, much easier to code against a dual-region GCS bucket because the bucket namespace and object metadata are strongly consistent across regions.

The semantics they are offering are very different from S3. In Colossus a writer can make a durable 1-byte append and other observers are able to reason about the commit point. S3 does not offer this property.

Sure, but that's not what the parent said.