OTOH, I can't see either of them being willing to take a veep slot for the other. Hillary didn't claw her way to the top of the ticket just so she could be overshadowed once again by a more popular and charismatic partner (remembering she'll still have to ride herd on Bill trying to turn her administration into his co-presidency 2), and Obama would have to be suicidal to agree to be just a heartbeat away from Hillary becoming president.
Yeah it’s not going to happen.