@hightor,
Interesting observations. Thanks.
I don't think the advantages of a Biden Candidacy in the eyes of Democrat leaders involves his skin color: rather it is (In my opinion) the fact that, unlike the large collection of other announced candidates, he wasn't presumed to be advocating crazy policies, likely to inflame opposition, and, equally important, would be seen by voters to have more gravitas than any of the others.
Unfortunately for both Biden and the party, the prominence gained by Sanders and his imitators has moved the discourse among Democrats so far to the left that Biden has ended up looking a little silly in his efforts to speak the new political language. Moreover in this same process the weaknesses that limited his own political aspirations (until being chosen as VP by Obama) have again been brought to center stage.
So far it looks to me that the forthcoming debates and competition among this group of candidates is more likely to drive the emerging party platform farther to the extreme left than to the more moderate outcome the party leaders may have hoped for.