Seems like you would at the very least need a fairly thick application layer on top of Postgres to make it look and act like a messaging system. At that point, seems like you have just built another messaging system.

Unless you're a five man shop where everybody just agrees to use that one table, make sure to manage transactions right, cron job retention, YOLO clustering, etc. etc.

Performance is probably last on the list of reasons to choose Kafka over Postgres.