The federal government could still retain control over the National Mall, and turn the rest of the District over to the people. Many of the federal agencies are in suburban Maryland or Virginia anyway, so federal funds are already going toward specific states to fund the operations of the federal government. And let's not even get into all the military bases that are located around the country, thus funding the economies of those various states.
Besides, the federal government is already sending a certain amount of money to this part of the country, regardless of whether you call it a "state" or a "district" or whatever else. So if it's a question of fairness it isn't like the other 50 states would suddenly be worse off.
Maryland doesn't want DC back, which is why DC should become a state. It's ridiculous that we have no representation in Congress despite the fact that we have MORE at stake in congressional decisions than any state does, since Congress can and does veto the actions of our city council for their own political whims.
I would like to point out that the reason why Washington, D.C. became a federal district in the first place.
It happened because back when Pennsylvania was the capital of the U.S. Veterans of the Continental Army was protesting that Congress hadn't fulfilled their promises to provide them with pay, and so they marched on Congress in Philadelphia. Congress asked the Philadelphia Executive Council to use the city militia to protect Congress. The Council refused, and so Congress had to flee the city to Princeton, NJ, for their own protection from the protesting armed soldiers.
That caused Congress to see the need to make a capital in which the federal branches could see to their own security needs rather than a city or state government. This is why Washington, D.C. is a federal district - they don't have to worry about a city or state government undermining them.
But, then again, our understanding of federalism has changed since then. Now, for the most part, federal power supersedes state and city power. Also, the federal government has federal police agencies (FBI, Secret Service, Homeland Security, etc.) that can work with or independently of local agencies, which renders the original need for it to be specifically a federal district moot.
So nowadays I think that Washington, D.C. would be better served with statehood. The federal buildings can still be administrated by the federal government but the local government would have more control over local issues, which would thus depoliticize their local issues. It would also give the people of Washington, D.C., representation in the federal government.