We could help ORMs solve the N+1 SELECTs problem and help them avoid transferring vast join projections unnecessarily. That'd make PostgreSQL pretty compelling for exactly the users we're mostly too busy dismissing to consider.
I'd be interested in reaching out to some Hibernate/JPA and ActiveRecord folks about how the DB could help the ORM and have been meaning to explore this area for a while, but -ENOTIME. If anyone pursues it I'll be really interested in hearing how things go.
Are those ideas on ORMs beneficial exclusively to PostgreSQL or to all DBMSs? I don't know the structure of ORMs allows for improvements to be advantageous to a specific DBMS.
Most ORMs have dialect layers for query generation, DB-specific customisations, etc.
Whether they're flexible enough to handle this sort of change - I don't know. That's part of why I'd like to explore the ideas with ActiveRecord, Hibernate, JPA WG, etc folks.