I dont recall any other state that became one via constitutional amendment.
The original reason for having a Federal capital district is so that no state would have power over the seat of the Federal government. The District voted for Hillary Clinton by something like 92%. Imagine the hostility of such a state government against President Trump. Look at what New York state government is trying.
“The District is specifically mentioned in two places in the Constitution. In the body of the document itself and in the 23 Amendment. Dont see how it can become a state without altering both parts where it is mentioned.”
Thanks!