We know that there is a capital city in each state. So D.C. becomes a "state", where would the capital city be?
A former men's room in the Capitol, now a multigender one. Room for a card table and another to count incoming tax money. Yellow tape border around it to mark it as a "city."
DC was set up as a federal enclave. The smallest states produce thousands of tons of food and have considerable manufacturing. DC does not.
DC is already the most over-represented part of the country. If it is made a state then the farmers of South Dakota who work 14 hour days during part of the year become less represented while those in DC who just eat the food become more overly-represented.