The SC will say it is not a violation of the 2nd Amendment, because it isn't. The District of Columbia is under the sole rule of the Federal Government, and not subject to the Bill of Rights guaranteed to the States and the People of those States. The reason they'll find it perfectly Constitutional is that they will fool most Americans into believeing that their ruling also applies to the States.

Then they can always lean either way...if the People swallow it, they'll let them be deceived. If the People start slaughtering Politicians in the streets, they SC will clarify and say "Nonono....not EVERYWHERE, just outside the States. Washington DC isn't under the protection of States Rights, silly people."

It's an experiment. Nothing more. Guns have been banned in DC for a long time...it's being addressed just to test the waters and see if We the People are ready to surrender our 2nd Amendment rights yet, or if they should wait a little longer to take those rights.