Hey, the federal district doesn't have any permanent residents exept the president and the FP*1 but that doesn't mean it's nonexistant.
The reason for the near-complete retrocession was because Congress decided that the federal government "should not have direct control over any land currently or in the future inhabited except needed to rightfully administer the country", so the federal district was limited to a small area containing the white house, capitol, mall, washington oblix*2, Smithsonian federal museum complex, and other federal buildings and monuments, and forbidden to have people live there aside from the president himself (and later the fp*1). If this failed then it is probable that the vast Western lands under federal control wouldn't have been ceeded to their respective states, though I imagine this would happen at some point anyway. At least, the great basin wouldn't be quite as environmentally devistated.
Washington county, Maryland wouldn't even exist, and as a resident of Georgetown city*3 in that very county my life would have been different too, I suppose. Maybe CAT*4 line five station: Georgetown would be finished faster if the feds could order the city to stop obstructing? Maybe the gca*5 wouldn't have two different distinct business districts in downtown Alexandria/Arlington and confluence city center*?
OOC:
*1 federal police
*2 Washington monument
*3 remains a city in Washington county due to lack of consolidation of otl DC
*4 capitol area transit, ttl's Washington metro. Somewhat plagued by nymbys
*5 greater capitol area