Google did have it mind because back in June Matt Cutts apparently said:

"Some have suggested that Google could disavow links. Even though we put in a lot of protection against negative SEO, there’s been so much talk about that that we’re talking about being able to enable that, maybe in a month or two or three.

What I am questioning is what happened to that idea, and if it is still in their minds, if is not in line with what Bing have done, what format could it take?
What perhaps could Google do different?