Easy legislation: "Any person permitted to carry a concealed handgun in a neighboring State, shall be authorized to carry in the District of Columbia" with the typical restrictions on carry inside federal buildings.
Immediately, anybody with a Virginia permit, or who qualifies for a non-resident permit which Virginia grants reciprocity, can own and carry in DC.
Couple that with the right to buy guns in any neighboring state, to get around DC's lack of gun stores.
Well, I think that since Congress has the power to legislate "in all cases whatsoever" for the District of Columbia, they are within their rights to exercise discretion over whether or not the residents of DC who are not citizens in a state may or may not buy, own, posess, or carry weapons.
But it's very surprising that Congress wants to exercise authority over state permits to carry but refuses to grant US citizens who are legal CCW holders in their own states the right to carry in DC. The excuse that "this was decided by the DC local government" is absurd, since tha "local government" exists at the pleasure of Congress. Congress could make DC "local government" cease to exist tomorrow (actually quite a good idea, BTW) without violating any part of their authority.