For certain scandals just losing control of an email address is enough to cause serious concern.
Willfully admitting that control was lost could be a story in and of it's self.
Email is not a reasonable means to conduct business, qwerty is a terrible keyboard layout, different countries driving on different sides of the road seems like a really silly thing to do.
Just because something isn't reasonable doesn't really hold much sway when it comes to will people use it.
How would the accused sender be able to prove it was or was not? And is it his or her burden?
Yes, individuals will use any reasonable to prove its authenticity. My point is that DKIM is not a reasonable means.