Plus, you can make "hybrid" tables in PostgreSQL that have some fields in separate indexable primary and foreign key columns (or other uses, as needed), but remaining fields shoveled into a JSON CLOB "column".

The E/R information between tables remains exposed and enforced, but the content details can be made fungible where desired. There is an extension to include JSON fields in queries, as well, though it won't be as fast as using a real column with an index on it.