Good luck getting 3/4ths of the States to ratify this. Ot is it 2/3rds? Good luck with that too.
Section 3 - New States New States may be admitted by the Congress into this Union; but no new States shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.
If a majority of Congress wants DC to be a state, that's what happens.
They'll carve out the Capitol, White House, and a few buildings as the Capitol District and the rest becomes a state with a simple majority vote in the House and Senate.