I’d consider it extremely unlikely. Taking a diff of a relational database is far from trivial, and the gains are minimal. If you’re running a large enough site to make app-level “delta backups” worthwhile, you’re probably going to be switching off Discourse’ built-in backups anyway, and using pg_basebackup+WAL archiving to hit your RPO targets (which, as a bonus, gives you point-in-time restoration capability).