Neither is it particularly novel that he releases it on a Wiki. Lots of large Wiki projects are flourishing, and it doesn't seem particularly strange to put a free book online like that.
What is novel is the way it has been done. Code v2.0 haven't just been dumped on a Wiki and left there to bitrot as happens to many works. It's been put out there with an explicit agenda, and a significant set of comments to guide a transformation of the book with a definite purpose.
I have read some of Lessig's articles, but have never read Code. Time to take a look, and who knows maybe I'll decide to try providing some input. Just because it's there. I hope this experiment succeeds, as if it does I'm sure more will follow.