I really don’t know how likely it is that he is Hillary’s VP choice. It’s pretty rare for a candidate to choose one of the also-rans as a running mate, when you look at the history. In this case I think she may be afraid of him upstaging her, and that the non-die-hard dems will look at that pair and think “So who’s actually going to RUN things, ‘cuz neither of THESE TWO can!”
Kerry-Edwards is the most recent example. Reagan-Bush.
I agree though that the tougher race he gives Hillary to the nomination the less likely he will get tapped as the VP candidate. However, if he is sitting on $100 million in a war chest, he is going to look pretty attractive.
My guess is she will go with Richardson for the Hispanic and Western state votes.
It is not usual, but Kennedy/Johnson and Reagan/Bush come to mind.
Kennedy chose Johnson in 1960.
Reagan chose Bush in 1980.
Didn't Mondale challenge Carter for the nomination in 1976?.