From what I've heard, it's merely an "Export as epub" feature, kinda like what Atlantis does. Useful, but you still can't edit the code or open epub documents. And the exported epub won't look the way it does in Pages since the feature set doesn't translate directly and different renderers are used. Again, useful in a pinch but as primitive as it can get.
Apple knowledgebase article about the new feature is
here.