I'm going to say not in the 21st Century, if ever. I could theoretically see the black vote becoming more Republican, but it wouldn't be uniform. For instance, it might make sense for Republicans to start winning rural Southern black voters, but that wouldn't make a huge difference in somewhere like DC.
As someone else pointed out, in order for DC to go Republican, the Republican would have to win 91% of the black vote nationally - because white voters in DC are still extremely Democratic, and make up 43% of the population.
These assumptions are absurd. They honestly take on a bit of an unintentionally semi-racist tone that Black voters would flip by the tens of thousands before their ideologically principled White liberal counterparts would move at all ... any Republican who won D.C. would improve DRASTICALLY with Whites.
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Well, it's hard to imagine a Republican improving so much in the white vote, nationally, that they win DC without winning a wide majority of the black vote.
Unless DC whites specifically swing much harder to the right that than white voters nationally, but I can't imagine a scenario where that happens because white voters in DC are clearly very inelastic, perhaps more so than black voters in DC.