According to Slate, “Choosing [Senator Elizabeth] Warren would be an uncharacteristically bold and thrilling move for the cautious Clinton, one that would help unite Sanders supporters behind her candidacy while throwing its feminist promise into high relief”.
I think it is unlikely that HRC would choose Sen. Warren as her running mate, but notice that if she did, and the Clinton/Warren ticket won the White House, there would be consequences for control of the Senate. Massachusetts has a Republican Governor who would, presumably, choose a fellow Republican to replace Sen. Warren in the upper chamber. True, an election for a replacement would follow in 145-160 days. But there’s no guarantee that the electorate would return a Democrat. As recently as 2010, Republican Scott Brown was elected to the Senate by the voters of the mayflower state. That fact alone might be a deal-breaker for a Clinton/Warren ticket. But if it’s not, control of the Senate might be even harder to predict.