Biden already has the AA vote. Harris or Abrams don't make much sense...consolidate a big, important voting bloc that you...already have?
Tammy Baldwin makes the most sense. Pretty liberal - to counter Biden's "centrist" critics. VP noms don't normally move the needle nationally, but can help at a state level and WI would be huge.
But, Biden isn't going to be running for a 2nd term. And I don't see Baldwin getting big national enthusiasm as the top of the ticket nominee in 2024. Maybe Warren, but she's 70 already. I wouldn't be surprised to see Gretchen Whitmer either, though she'll face similar centrist critiques. Klobuchar, to me, is just not very exciting.
So, I don't know really. Baldwin makes the most sense for winning 2020. If Biden sees himself as a bridge from Trump to a younger Pres. nominee in '24, then Harris or Abrams, though there'd be huge reservations about Abrams having not ever been elected statewide.
I guess my list would be, in no order: Warren, Harris, Klobuchar, Baldwin, Duckworth, Yates, Abrams, Sinema, Whitmer, Rice, and let's not forget...he left open the possibility of nominating a Republican lol