I can see the potential benefits of using SideWiki. As Clay Shirky said, "Every webpage is a latent community".
As far as robbing bloggers of their comment space, Google Notes can do that. Facebook does that. FriendFeed does it, etc. It's not new, and I'm not sure that it's evil. Moving power to the edge isn't just about moving it to the authorspace, be it the New York Times, or BuzzMachine. In my case, it's about moving the power to me as a commenter. And I'm just as much on the edge as the Author.
If nobody whips up a integrated comment system for WordPress and Blogger that uses SideWiki as the engine, I'll be surprised.
A quick search through the API looks like there's no way to use the API to insert comments yet, which could be a roadblock. And the fact that comments are voted up instead of threaded pretty much kills it as a discussion space.
However, I'm cautiously excited about what this may evolve into.
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