As Biden's lead in the polls grows, it seems to me there's less importance for him to choose a VP candidate who can add enthusiasm to the ticket, specifically a black or Latino. The closer we get to the election it seems the more we can count on his opponent to provide enthusiasm.
So maybe there's a case to be made to go in another direction--a VP who would be great at improving the way the government operates. That would represent a long-term investment in government capability, which is the prerequisite if liberals are to succeed in their ambitions for government programs.
If you accept the premise, it seems to me that two possibilities stand out: Elizabeth Warren and Gina Raimondo. The case for Warren seems obvious to me; the case for Raimondo can be built based on her track record, specifically with covid-19, as laid out in this Politico piece.
[update--to clarify "operations VP"--it's the sort of role Biden performed with the stimulus act, and Gore performed with Clinton (though I'm not really a fan of Gore's effort.