Arguments against DC and Puerto Rico statehood that rest on political calculation (more Democratic senators and Congressmen) remind me of the antebellum period where new states had to be balanced between slave and free ones. Now it has to be balanced between red and blue; the divide is almost as stark.
A solution would be to find a red territory to admit at the same time. I can't think of any, so how about instead the GOP just stops alienating Latinos and African-Americans so they won't view DC and PC as safely Democratic. Every state in the nation has had a senator and congressmen of both parties, even Alaska and Hawaii. PC and DC wouldn't be exceptions, unless the GOP wants them to be (they've never won DC in a pres. election
).