Believe it or not, one of the current at-large seats was held by a Republican as recently as 2008 (albeit a socially liberal Republican, but a Republican nonetheless). There are also currently 2 Independents elected from the at-large seats. It's a possible that as a state, it could develop a unique party system, although with the Democratic Party still dominant.
It's in D.C. law that of the 2 at-large seats, Democrats are only allowed to hold 1 of them. Now how that stands up to a court challenge, I have no idea.
If it was going to develop a unique party system, it already would have. The Republicans are still the 2nd-largest party in the district and it's considered a complete non-entity by outsiders.
