I know we've talked about this at conferences from time to time and so I thought I'd share what I learned at one of the keynotes at OSCON.  Martin Fowler gave a great talk about internal architecture in our open source projects https://opensource.com/life/15/7/never-neglect-your-projects-architecture and mentioned this article: http://martinfowler.com/bliki/DesignStaminaHypothesis.html