If Warren were looking to shore up the base, she'd pick someone for VP with significant party support whose supporters are largely reluctant to support her, but the whole reason she's winning is that that person doesn't actually seem to exist. She's the consensus pick.
So really it's kind of an open field. Obviously, if she's going to go for a strong anti-corruption pitch, anybody already under investigation for anything that could possibly be legit is out (sorry, Gillum). Probably best to avoid the Northeast for demographic reasons, and no machine states. Florida, NC, PA, Texas, or Arizona would be my home state picks, preferably black or latinx. I think people are wrong about an all-female ticket being a mistake, btw. Once you've put a woman on the top of the ticket, anybody reluctant to vote for reasons of misogyny isn't going to be swayed back by a male VP, or pushed into opposition by a female one. That die's already cast.