The Supremes will duck the issue by ruling in favor of DC per article 1 sec 8: “To exercise exclusive Legislation in all Cases whatsoever, over such District ...” while leaving the 2nd amendment intact.
That’s my worry too.
DC is kind of like Guam/Virgin Islands. And kind of like a military base in a way.
And Congress is the base commander.
Can civilian workers on a military base carry their firearms around without permission from the base commander?
The District of Columbia, and the territories, are covered by the Bill of Rights (including the 2nd Amendment). The Bill of Rights limits the federal government’s authority, and the federal government has ultimate authority over D.C. and the territories. Hence, those areas have a RKBA just like the People of the several States.