Notch, creator of Minecraft, is developing a rendering engine for Doom in Dart and WebGL (I assume as a hobby). I am a little late to the party, and he has been developing for the last couple of hours now. If you were curious about what it looks like to watch someone develop a 3D rendering engine, this could be your chance. He also interacts with the chatroom, which should be more interesting.
Watching people program is picking up in popularity. While you would think that this is even more boring than watching people play video games, and you might be right, it could still gain an audience. Epic Games has been working to develop Twitch streaming capabilities directly within Unreal Engine 4's editor, to allow indies (or even large developers) to interact with fans and colleagues.
If interested, check out Notch's stream at Hitbox.tv.