AOC would work fine. She’s still like the most beloved outside Sanders for that wing of the party. I’d say Ellison, but Biden committed to a woman (which I think is a huge mistake btw because it limits options and comes off as virtue signalling) so he can’t go that route
Honestly if I was Biden, I wouldn’t nominate someone under the guise of a progressive olive branch. That requires a concession on his end to make it meaningful that I don’t think his camp is committed to making.
He’s better off trying to play the cards he’s dealt at this point. Go Whitmer. She’s a woman, she shores up a must win swing state, she’s attractive so she’ll play well with the shallow American electorate, she’s a Midwesterner, she can campaign on Trump’s covid response which I think will be a hurdle for Biden to do himself.