For now, BemiDB supports only full Postgres table data re-sync. We plan to enable real-time data syncing from Postgres into S3 by using logical replication (CDC), which is much more reliable than PG NOTIFY.
We use logical replication and this exact approach with our other project related to auditing and storing Postgres data changes https://github.com/BemiHQ/bemi. We're thinking about combining these approaches to leverage scalable and affordable separated storage layer on S3.
Lmk if that makes sense or if you had any more questions!