I'm the author of 12factor (although really it is an aggregation of the work and insights from many people at Heroku). It continues to surprise and please me that this piece continues to be relevant eight years later—a virtual eternity in software/internet time.

Fun fact: I debated whether to call it "the Heroku way" or somesuch. Glad I went with a standalone name, feel like that allowed it to take on a life beyond that product. For example I doubt Google would have wanted a page about "Heroku Way app development on GCP" in their documentation. :-)