I'm curious if EnterpriseDB already implements this.
The closed-source PL/SQL emulator that they sell on top of PostgreSQL (and license into IBM DB2) is something that has drawn occasional interest over the years.
Yes, EnterpriseDB implemented it as part of their Commercial Postgres derived database : PPAS. It is not Open Source, whereas, PG_DBMS_JOB is Open Source and released under PostgreSQL license, which is the most liberal license :)
It is the extensibility of PostgreSQL that makes this possible.