The new version of ISO 8601 is being prepared for final ballot and is now expected to be published in mid-2019. There will be two parts. Part 1 is essentially the same as 8601-2004 (with some corrections). Part 2 is extensions. There are many extension, including EDTF functionality (some syntactic changes were necessary, to satisfy international requirements), and in addition, EDTF is included as an ISO 8601 profile.
The draft specification from 2012 has therefore been superseded and a revised EDTF Specification based on the revised 8601 is now available.