I'll sum it up in one word: anger. If anger boils over on the left, they'll want a way of giving the middle finger to the DNC first, then the right. It's not just black millennials. I could see lots of young people going for him if he talks a tough enough talk.
Granted, that wouldn't be enough for him to beat another candidate one-on-one, but Democrats will probably be lining up to take on Trump, so the establishment/not green tea party vote could get split between a ton of candidates, which might make Kanye's base the biggest. I could also see Kanye as having the most enthusiastic supporters, which would help him in caucuses (assuming that those still exist in 2020). Yes, Democratic super delegates would rather sell their soul to the devil than get behind Kanye, but they'd need to get behind one other candidate en masse, rather than being split among several.
I'm not saying it's likely, but it would be foolish not to take his bid at least somewhat seriously, and try to get behind someone else before it's too late. Never underestimate the ability of people to make irrational decisions when they're angry. Case in point, the 2016 election.
Well I'd say that the main beneficiary of anger against Trump likely wouldn't be a guy who admitted he didn't vote and said he would've voted for Trump if he did.
anger is rarely logical
you wouldn't have expected the main beneficiary of anger against (((globalism))) or w/e to be the billionaire who owes nine digits to the bank of china and goldman sachs and has been bailed out twice by a saudi prince, and yet…