WordPress is an open source blogging platform, which (amongst other things) means that everything is built out in the open. You can freely follow along or even participate in development.
If you’re curious about what’s going on under the hood, the best thing to follow is the WordPress Trac. This is where all of the magic happens, bugs and features are submitted, discussed, and acted upon all through this one site. Of course, if that’s a bit too much code and you’re looking for a more toned down highlight-oriented news and discussion blog, check out the official WordPress Development Updates. Here, you can follow along on major issues or changes. Think of it a sneak peak to the future of WordPress.