Are there any examples of other countries moving their capital because the city's unpleasant to live in?
I can't think of any off the top of my head. I can't possibly believe that DC in the late '80s* was worse than London in the Victorian era, which saw pollution, murder, human degradation, and, who could forget,
the smell of poop, permeating the daily existence of all residents, high and low.
If nobody in parliament thought to propose that they heard, "Winchester was pretty nice" during a cholera epidemic, well then I think DC's chances are pretty good.
*I was young, but I lived in MD at the time and visited the city frequently. Time is supposed to soften the edges on things and apply a rosy glow, but it's pretty clear in my mind that the city was just much, much, MUCH worse then than now. We may risk losing a lot of character through gentrification, and should work to stop it, but gentrification is better than whatever DC had in 1989, lemme tell ya.
And I only visited the nice parts.