There is speculation that Clark is a placeholder for Hillary, but that's nonsense, I think. He doesn't seem like the type to hold her coat, even if he did get the VP slot out of it. And Hillary wouldn't take the VP slot if Clark offered it. Been there; done that. (If you try to tell me that Gore was Clinton's real VP, remember: Gore got to go to funerals; Hillary got to design the health care proposal.
If nothing else, an interesting few months await us.