They just did https://news.ycombinator.com/item?id=42211280 (Amazon S3 now supports the ability to append data to an object, 30 days ago). Azure has had the same with append blobs for a long time. It's still a bit more raw than S2, without the concept of record. The step for a cloud provider to offer this natively is very small. And with the concept of a record, isn't this essentially a message queue, where the competitor space is equally big? Likewise if you look into log storage solutions.
(Founder) Both S3 Express _One Zone_ appends and Azure's append blobs charge the regular PUT price for appends. It may work for you, but probably not if you want to do smaller writes.
Blob stores will also not let you do tailing reads, like you can with S2.
In AWS, S2's Express storage class takes care of writing to a quorum of 3 zonal buckets for regional durability.
I doubt object stores will go from operating at the level of blobs and byte ranges, to records and sequence numbers. But I could be wrong.
