Elizabeth Warren will be the first female Vice President this November. She is CLEARLY interested and her attacks against Donald Trump are very convincing. During this last interview, she is really talking Hillary up. She wouldn't be doing this if she didn't want the job. The Democrats will want to make a splash. People who aren't voting for Hillary because she's a woman are not going to change their minds if she picks a man as her VP. And the Democrats would be able to take back the Massachusetts senate seat which is really important right now. Clinton/Warren 2016
I imagine there are probably plenty on the fence who might otherwise vote Clinton at the last minute, but if she picks Warren would see her as playing identity politics and secure those votes for Trump. I personally think she has more to lose by picking Warren, given that she won't even pick up the Sanders crowd since Warren was already demonized after Massachusetts.