I built a service using LISTEN/NOTIFY a while ago, but the fact that Postgres will instantly drop all messages to a given channel if there are no registered listeners made me nervous.

This felt like a big caveat to me, taking what could be an extremely well-guaranteed approach (e.g. a db trigger that writes a row to an event table, which is being polled by an application process) into an ops risk, where transient network issues could result in data loss. You’d want idempotent tasks and zero-downtime deployments, but it feels like the benefits don’t really justify the risk. If you want a topic exchange just have the polling process forward to a real message broker.

I like the concept of sending messages straight from the db, and we did run my service in production (for non-critical stuff), but unless something has changed with the way this works I would still be wary.