I like it.
The seat of the Federal government could be shrunken down to a small polygon containing the Capitol, White House, SCOTUS - I would want the Washington Monument, Lincoln and Jefferson Memorials in there too.
But yes, one state running from Baltimore City to Prince William County.
It would require approval of the Maryland and Virginia legislatures and the Congress.
I don’t think it would require approval of the states involved. You can’t make DC a state without a constitutional amendment anyway. So the provision that requires state approval would be overrriden as well when you amend the Constitution.