If a Gore 2020 platform contains both single-payer healthcare and the abolishment of the electoral college (in addition to his trademark environmentalism), the Dems may have a chance at unity.
He's also probably the only candidate who could make "Hindsight is 2020" his slogan and make it work.
He shouldn't make such a personalized slogan. Reminds me too much of "I'm With Her". Something like "A Return to Decency" would be better. The Democratic ticket of 2020 needs their equivalent of MAGA - something vague, universal, and empowering.
On paper, the "Hindsight is 2020" slogan (which I don't necessarily support) would work for any Democrat trying to make the election a referendum on Trump. With Gore the only difference is it makes the election a referendum on essentially the course of American politics since 2000, something I think liberals would be able to get behind.
Many of said liberals don't (or won't) even remember that election since it was idk, a generation ago.