Is is possible that PostgreSQL will replace these building blocks in the future?
- redis (Caching)
PostgreSQL has its own caching. It might not be quite as effective as redis', but you can us it if you are willing to take those trade offs.
- rabbitmq (amqp)
PostgreSQL has its own system for this, and other ones can be layered on top of fully transactional tables.
Again, you can use one or the other, depending on your needs, if you are willing to deal with the trade offs.
- s3 (Blob storage)
No. You can certainly use PostgreSQL to store blobs. But then, you need to store the PostgreSQL data **someplace**. If you don't store it in S3, you have to store it somewhere else.
