This is the first commercial game I can think of taking this step while the game is still live. All of the Ryzom source including tools, client, and server codebases are fully open source free software. For more, see the FAQ. It sounds to me a lot like a MUD codebase, and that makes me smile.
I do not see this helping them in the marketplace, but I’d like to see this become a trend. I have a lot of old PC games which are no longer playable due to DRM or other online components which no longer exist.