This is interesting question with at least couple options. So, let's dig in…
Apparently it's not going to happen.
I'm leaving the post here anyway, as I hope the code will resurface as extension, on PGXN maybe?
On 14th of May, Stephen Frost committed patch:
Add pg_audit, an auditing extension This extension provides detailed logging classes, ability to control logging at a per-object level, and includes fully-qualified object names for logged statements (DML and DDL) in independent fields of the log output. Authors: Ian Barwick, Abhijit Menon-Sen, David Steele Reviews by: Robert Haas, Tatsuo Ishii, Sawada Masahiko, Fujii Masao, Simon Riggs Discussion with: Josh Berkus, Jaime Casanova, Peter Eisentraut, David Fetter, Yeb Havinga, Alvaro Herrera, Petr Jelinek, Tom Lane, MauMau, Bruce Momjian, Jim Nasby, Michael Paquier, Fabrízio de Royes Mello, Neil Tiffin