I can’t see it being Newsom. He’s a white guy. And California is already in the bag for the Democrats. So what can he bring to the table?
If given the right odds, I’d bet on Michelle Obama. True, she’s lazy. No matter. She could act like one of those European heads of state. Don’t do anything except represent the country at formal affairs. Let someone else do the actual governing.
So if they dump Biden, I'd expect Newsom, Whitmer, some other governor, or maybe a senator. If they pick a white male, then they might put a black female (other than Kamala) on the ticket--Val Demings might do the least damage in terms of scaring away white voters. Hopefully Buttigieg would not be seen as a viable nominee. Hillary would be happy to accept the nomination but there are probably too many Democrats who would resist that--after all, she blew what looked like a sure thing in 2016.