Agree. The new wide event pipeline should fully utilize cheaper storage options-object storage like S3. Includes both cold and hot data and maintains performance.
I'm totally in favor of cold storage. Just beware of how you are storing data, the granularity of the files and how frequent you think you'd want to access that data eventually in the future, because what kills in these services is the API cost. Oh and deleting data also trigger API costs AFAIK so there is that too...
HDD-based persistent disks usually have much lower IO latency comparing to S3 (microseconds vs hundreds of milliseconds). This may help improving query performance a lot.
sc1 HDD-based volumes are cheaper than S3, while st1-based volumes are only 2x more expensive than S3 ( https://aws.amazon.com/ebs/pricing/ ). So there is little economical sense in using S3 over HDD-based persistent volumes.
