The fact this is out there is a warning for Barack. It shows that Hillary isn't worried about him (or the Democrats) winning in the fall; she's worrying about her own future and she's willing to play hardball in order to secure it. That should set off alarm bells all throughout his campaign, although doubtless his people are already painfully aware of it.
If Barack puts Hillary on the ticket, it's a serious admission of weakness -- if he can't stand up to the Clintons, what's he going to do with Kim Jung Il and Mahmoud Ahmadinejad? But if he keeps her off the ticket, what's it going to do to her supporters?