Other Postgres-specific features, such as foreign data wrappers, are near-unusable within Rails when you're committing your schema -- `schema.rb` ignores them, and `structure.sql` encodes information that should never be committed, like database passwords.
I don't think that Rails maintainers should be obligated to maintain `schema.rb` dumpers for a lot of different, esoteric database-specific features. But right now, if you want to extend `schema.rb`'s functionality, you need to monkeypatch Rails internals; it's fragile when upgrading.
I'd like there to be a stable, external-facing interface allowing folks to extend `schema.rb` dumpers with database-specific features, without monkeypatching. I'm happy to take on the work of implementing this, but I wanted to raise this as an issue first so that if the core team isn't interested in this as a feature no work is wasted.