Over the last few months I've had a gig working on a modified WordPress installation. My initial reaction to the codebase was disdain, one that I suspect many web application developers might share: it's certainly not MVC, it seems a bit hodge-podge, and it takes a bit of getting used to.
On the other hand, there's no denying that WordPress is a very successful project. It not only does its job well, it's possibly the most popular piece of software in its niche, there's an active theme and plug-in ecosystem, and it's widely extended and modified as a base for other sites. There are clearly more sophisticated products out there and yet WordPress seems to thrive.
In light of this, I'm looking for discussion or literature on WordPress not just as a product but as a project. I'm interested in both software design and project/process/meta choices (documentation, feature choices, community engagement, etc). Have you seen anything out there on the topic?
While I'd consider references to longer studied works ideal answers to my question, I also welcome your thoughts and commentary in-thread.