This may sound crazy but I think by 2070 most all states will have circulated through the “swing state” cycle whether or not they are blue or red. With the exception of like DC or KY lol.
But in 2070 specifically maybe ILL, HI, NY? Maybe CA idk, it’ll probably be a traditional lean/ tilt D state.
KY is far more likely to become a swing state again at some point than DC ever is to come close to voting Republican, short of a massive realignment.
A state like WY or something would be a more appropriate parallel to DC, as it doesn’t have much history at all of voting for Democrats on almost any level.
But really, there is no state, blue or red, comparable to DC in partisanship.