It all started with a comment by Rioriel on WoW Insider and a push in the right direction from Marlamin. With an older bit of code that does a rough implementation of what we wanted for this (and something I already had in mind), work started.
Fast forward to today. New system for static map generation supporting different renderers (will be opensourced), static map creator on the website. Rioriel had a shot with it, became very enthusiastic about the tool and started adding location data to his posts on Postcards From Azeroth.
So from today Postcards From Azeroth are visible on the World of Warcraft Map and Postcards From Azeroth show their location under the postcard: