Maybe Jamal wants Harris to make history by becoming the first female president of the US. And Joe will also be remembered by history as the man who made it happen. The idea is not for her to accomplish anything but to make history, that's all.
And still, I don't think it would be well received by an important percentage of the voting population of the country, to be honest. If there is something clear from this election is the fact people is getting fed up with the current path the democrat party is taking, and one of the components of that path is identity politics (some people call it DEI, as well) the idea of giving Kamala Harris a special treatment because she is a woman and she has a different color of skin would only show how tone-deaf the party has become on the subjects which actually the people of the USA care about: the economy, being able to save money and the way the federal government spends taxpayer money abroad.
I believe it would be completely dumb if the Democrat party allows such a thing to ensue and further throwing their credibility down the drain, more people would end up getting away from them.