[masklinn]

Which is pretty much what you want to build a schemaless nosql-on-postgres.

Also, Posgres already has hstore (already mentioned) and XML columns, which are schemaless and "unstructured".

[zapov]

Well, I'm arguing that flexible schema is better than no schema. And in practice schemaless is only about schema defined outside of database. It's a solution to the wrong problem.