There are a number of possible resolutions to giving state citizenship to the residents of Washington, DC. Here's an overview of the issues. All solutions I've seen carve out the area comprising the federal buildings, but not the population of the DC area.
Briefly,
* Make WDC the 51st state
* Give the land back to Maryland or Virginia
* Give WDC semi-state status with voting rights in Congress. Different proposals have been discussed.
Reasons given to oppose,
* Making it a state would add to the Democratic Party membership in Congress.
* The state would be 3rd smallest by population, adding to the imbalanced influence of small states on Congress and the electoral college
* The federal government would be surrounded by the new state and dependent on it for services and commerce
Yea or nay?
Give the land back to Maryland would be in keeping with existing precedent. Arlington County, Virginia
used to be part of Washington D.C. prior to being ceded back to Virginia by the Federal Government. What remains is the Maryland portion.
But that doesn't resolve the issue of the "Federal reservation" containing the highest echelons of the Federal Government then falling largely under the jurisdiction and control of the state of Maryland. Granted, there are other examples for department branches being headquartered outside of Washington D.C.
I guess another option is the process of returning Washington D.C. to Maryland while the Federal Government begins the process of selecting a new capital selection process, where a new Federal District is constructed from
bedrock up at a new location which a new grouping of states have agreed to cede to Federal Control. Only this time "the federal reservation" will
not play host to permanent residents so as to avoid the issue in the future. Likewise, all land within that "reservation" will remain property of the Federal Government, private property will not exist in the Federal District 2.0 much like the case in many Military bases across the country.
There may be housing constructed, it may even be "leased" out for third parties to manage and maintain, but only Federal Employees(on "temporary assignments"), Elected Government Officials, and foreign diplomats would be allowed to obtain occupancy.
Edit: Of course dissolution(/reconstitution elsewhere?) of Washington D.C. as a Federal Entity then creates some "interesting" constitutional questions in other ways.