[El Gato]

They could restrict the federal government's power to regulate firearms without touching the state governments' power to do so.

They could, but they'd have to rule that the right was not a fundamental one, essential to ordered liberty. But if they do that, they would also be likely to allow some or all of the DC restrictions.

[robertpaulsen]

"but they'd have to rule that the right was not a fundamental one"

I think that's why they took the case. The DC Circuit Court ruled it a fundamental right, and I believe the U.S. Supreme Court will change that.