There is absolutely zero chance Kanye will win the 2020 election. Not even 0.000001%. Which party is going to give him the nomination? The Republicans have Trump. The Democrats have Biden. Kanye would have an awful lot of trouble just getting his name on any ballots, let alone winning a state's Electoral College votes.
As for how bad he'd be: the last person America needs in the office is another blowhard with an ego the size of a moon. Kanye has neither the discipline, not the intelligence nor the curiosity to handle the role. The only thing that would make him better than Trump is that he's not pure evil.
That said, Kanye has allowed himself to be a Trump tool before. This certainly looks like it's happening again; any votes for Kanye, in Trump's opinion, would obviously come from Democrats, not Republicans. But I don't expect it even to get that far.
For better or for worse, the ONLY way to become President right now is to win the nomination of either the Republicans, or the Democrats. It seems the Republicans are much more likely to be attracted, like a moth to the flame, to celebrity, and the current Republican tent is constantly dwindling, as people horrified by the shocking racism and anti-professionalism are leaving. Trump, like an angry older, white man, was able to appeal to this demographic. In fact, he's been the reason why this group is dominating the Republican Party more than ever. The Republicans who are left would not vote for Kanye — they will use him, but never put him in charge.
The Democratic coalition, on the other hand, is far, far, far more diverse. The Democrats have the Black and Latino communities, as well as others, and many white women. Professionalism and competence and qualities like having good intentions actually matter to them.
Kanye's an only realistic possibility would be as a third-party candidate, but third parties just don't have a chance in the US system, built, as it is, with structural advantages for Democrats and Republicans together, as opposed to third parties. Without capturing the hearts and minds of the thousands of volunteers and donors in one of the two major parties, no one has a chance, not even a celebrity.
As for Kanye, I do not expect him even to try to become President. Even if he really did enter the race now, he's far behind the two main parties and candidates in spending, research, hiring, vetting, and preparation. He won't be able to get on many ballots. So why the announcement? Honestly, I have to wonder if Trump put him up to it. Trump is hoping to either intimidate, prevent, or else lull with a false sense of security Black voters into not voting for Biden. That's his plan. And Kanye is either willfully and knowingly participating, or else he lacks the insight necessary to understand the seriousness of what is happening. Neither option looks good for him.