It's been 40 years since they were granted electors, and the Democrats have won it in a landslide each time, obviously beause the urban population.
Is it possible that the district's three electorial votes will ever go to a Republican canidate?
Congress has the authority to determine the manner by which electors are appointed (they have the same role as a legislature with respect to a State's electors). So Congress could appoint 3 Republican electors. This is more likely than 3 Republican electors being elected by the voters.
More likely to happen this year, I grant you that. But we're talking tiny fractions of a percentage point here.
In the long run, a complete realignment is not impossible. It's happened before in America, might happen some day. Alternatively, DC might become all gentryfied and the ghetto people are all forced to move to Maryland. While, in the current alignment, the city would probably still be (comparatively marginally) Democratic then, it could go Rep in a landslide.
Give it enough time, and I think either development will become more plausible than your "legal coup" scenario.