The project was started 1,5 years ago at the time of writing the article.

Demiurge · on April 30, 2015

I've been using Mapnik for about 8 years now, I think, since it was the first alternative to MapServer. OSM has always been using Mapnik, with mapnik styles in CartoCSS for a long time too (http://wiki.openstreetmap.org/wiki/CartoCSS). TileMill beta (https://github.com/mapbox/tilemill/tree/v0.5.1) came out 4 years ago. So, I definitely would have made the same recommendation 1.5 years ago. It still came out pretty cool :)

Feel free to ask me any gis or web mapping questions as demiurge@irc.freenode.org, I'd love to facilitate more beautiful maps out there.