If you look at the history of DC, I think the founders had a fear that having a federal capital inside of a state would provide some sort of an unfair benefit to some state. I think in 2021, we can get past that fear. I think the idea of just absorbing the District into the existing states of VA and MD makes sense, and would solve all of the problems for the residents of DC, without creating any of the political fall out.
PR is a different story.