I’m with William Tell. DC has argued that the Second Amendment only applies to members of the National Guard, that is, the “state militia” (which DC lacks). That’s where it’s from. SCOTUS will affirm or reject that, on its face. If it’s rejected, the collective rights interpretation is dead, and notwithdtanding the narrowness of the ruling, gun laws everywhere will then be open to challenge: if it isn’t a collective right, it’s an individual right, which innumerable state and local laws violate.
I hope you’re right.