1. The nation's capitol was not supposed to be in a state, owned by a state, or be a state because it would have drastically more power than any of the other states. That alone should eliminate it from consideration.
2. The nation's legislators were not supposed to make Washington a permanent home. They were supposed to ride into town, do their work, then go back home and listen to their constituents. In today's world, there's no need for them to even ride into town any more. Get them back to the people instead of the lobbyists.
3. Anyone who lives in Washington decides to live in Washington. If they want to vote, they need to move to a state so they can. Or, failing that, there should be no permanent residents in Washington. If they want to live there and still vote, they should be assigned residency in whatever state is closest to where they live, and their taxes and votes go to that state. No way should Washington become a state.