I can't see any electoral advantage to picking Susan Rice. The average voter has no idea who she is.
There's none for picking Heels Up Harris either.
Typically Presidential Candidates pick a VP running mate from a state they might not otherwise win in an election. Heels Up Harris doesn't deliver anything to the Biden Campaign. If anything, he alienates a large chunk of the black vote due to her overzealous prosecution of pot cases in Commiefornia.
If he picks Susan Rice, the only thing she brings to the table is ... well, I cannot think of anything other than someone who knows the ins and outs of Obamagate (Lord knows Biden doesn't remember sh*t) and will direct the future cover-up.