The documentation makes reference to an announcement on the blog, which doesn't seem to be available. If anybody wants to keep watch, be my guest: http://blog.getbootstrap.com.

I've been keeping an eye on the pull request (https://github.com/twitter/bootstrap/pull/6342) and the gh-pages branch (https://github.com/twitter/bootstrap/tree/gh-pages) for other Bootstrap 3 information.

http://twitter.github.io/bootstrap/customize strongly suggests there will be another RC after this one.