Here is the conclusion from a National Review article about DC representation.

Serious advocates of congressional voting rights for D.C. understand that they have three options: constitutional amendment, statehood, and retrocession. Each is difficult but not impossible. The 23rd Amendment, granting D.C. electoral votes, was ratified in 1961. (If the folks behind the current bill are right, the amenders were chumps to go to the trouble.) Yet an effort to amend the Constitution to treat D.C. “as if it were a state” fizzled in the 1970s. Formal statehood, achieved through the rules of admission established by the Constitution, is possible but politically unlikely. Finally, there is retrocession — i.e., ceding the bulk of the district to Maryland, much as a portion of D.C. was ceded to Virginia in 1846. A federal district would survive, but as a much-reduced core that contains the Capitol, the White House, and the National Mall. In some ways, this is the most attractive option. Maryland, of course, would have to agree to the transfer.