Does Harris fit the bill? Is she seen as progressive enough? I don't know if Bernie supporters are enthused about her?

I think the ticket needs youth, competence, and racial / gender diversity.

POC saved his ass. Not picking one would be a real slap in the face

Biden is an East Coaster so Harris is out. We need someone from the middle.

Someone who will be in a lockstep with his ideas. So, again, no Harris, no Warren. Someone who, if called, will be able to immediately continue with Biden's ideas and will not try to sneak own agenda.

I think Harris is still an option. African-Americans saved our asses from disaster so we should definitely pick an African-American woman.

I was initially for Kamala Harris in the Primary, so I'd be happy with her. But you don't think Biden needs help with African Americans. I think she appeals to a MUCH broader group then just that voting group, would excite the younger voters (and maybe help them get out and vote?) and would clearly be ready to become President, if the time arose.

...preferably in Medicine.

but the idea of balancing with a progressive advocate is another good point.

be to him what he was to Obama, able to take on a full portfolio and run with it.

The conservative Republican party still has a very hierarchical structure and ideology, rule from the top, and their VPs are still expected to attend funerals and helicopter to golf dates. Thus choosing people like little Danny Quayle who checked the boxes for advantageous home state, white skin color and male gender makes sense.

But our egalitarian Democratic Party has advanced with the times. Our are chosen for their desire and ability to do important work, not go into semi-retirement or posture at appearances in Nancy Reagan-style devotion.

And, of course, being a spare who is genuinely capable of being a good president has always been important, but with the oldest potential president in history that ability has a spotlight on it. But that means the spare should be someone who would fulfill what the electorate voted for. Used to be the VP could even be from the other party to "balance" and get support of some faction.

For all these reasons I like letting our presidential candidates choose their workmates and potential replacements, and decide on what balance will work overall.

#1--the VP must be ready to president on day one.

#2--If we're looking in terms of shoring up Joe's weaknesses with voters, he has a problem with voters under 45. But he can't just pick any candidate who "appeals to people under 45." Voters under 45 for the most part tend to be highly progressive. He needs a choice like Warren, who is the leading female progressive voice in the party and a national figure to bring those votes in. If he wants young, progressive voters to turn out in November, he has to give them a reason.