No, Postgres has supported those for a long time. For example:

    SELECT *
    FROM   employees e
    WHERE  EXISTS (SELECT 1
                   FROM   employee_projects ep
                   WHERE  ep.employee_id = e.id
                   AND    ep.project_id = 5)
    ;

This new feature is a lot like correlated subqueries except you can put that nested SELECT into the FROM clause and still access the employees table.