We’re now previewing the addition of PostgreSQL compatibility to Amazon Aurora. This edition has the benefits customers have come to expect from Aurora, including high durability, high availability, and the ability to quickly deploy low latency read replicas while supporting the full SQL dialect and functionality of PostgreSQL 9.6.
I should have been more clear. I was referring to storage auto-scaling. Aurora gives you access to up to 64TB of disk billed in 10GB increments. You don't need to preallocate and manage the scaling of your disk as you do with RDS.
It could be a very performant transparent caching layer when combined with the fdw extension[1]. You can push down the true analytics queries down to Redshift, but cache the resultsets, rollups, facts tables, etc, in materialized views. Then have the full power of modern Postgres available for exposing your data warehouse. The more predictable performance and auto-scaling storage makes it much better than the standard RDS for that setup.
Based on your numbers the difference in pricing between Aurora and Postgres ($4.64 - $3.98) x 24 * 30 = $475/mo. To the company using a db.r3.8xlarge, which has 32-cores and 244 GB of RAM, that's not even a rounding error.
For many installations, an Aurora read replica can eliminate the need for a multi-AZ master instance which cuts the cost of your master instance in half.
