Why do you want Module#mix in favor of Module#prepend. The former introduces a whole new system for mixins alongside the old one, while the latter simply makes the existing system work for extending existing classes (a first-class, no caveats alias_method_chain)
I wasn't really flying the flag for Module#mix, just intrigued as to the pattern of things making it into head and then either making it out into tagged releases (or not).
That said, I confess I was a fan of mix, but it might be in my favor for things to get more complicated sometimes.. ;-)