I went from wishful thinking on this to being almost sure of it, and here's my supporting argument:

1) He's being overexposed on TV right now. Seems like the Democratic party really REALLY wants to make sure that people remember who he is.

2) Look at these polls: https://abc7.com/post/election-polls-what-8-potential-kamala-harris-vp/15099930/

Highest favorability among the base by FAR, and rallying the base is high priority at the moment. Second place on favorability overall, and more importantly, the only person polled where 60 % actually HAD an opinion, which means he's the highest profile choice.

3) As a former presidential candidate himself, he's already fully vetted - far more than anyone else. And there's only 11 days left to pick.