I'm happy to change my mind if I see the evidence.
As of right now, it mostly rests on an assumption that white people will flee because they now do not want to live near black people. Rural denizens can't fathom why anyone would live in a city in the first place. But cities all over the country have been booming for quite some time, and there is little reason to believe that COVID or BLM will change that.
We'll see.