No chance in Hell that Biden picks a white woman. Blacks would go ballistic and not turn out.
If he was going to do that, he might as well pick Warren and keep more of the Hard Left on board. Focus groups have probably told the campaign that picking an angry black woman is poison at the polls, and will drive away Hispanics. This will always be the major problem for the Democrats, who are a collection of socio-economic subgroups who hate each other only marginally less than they hate their fictional “white oppressors.”