It explicitly didn't consider foreign intelligence surveillance power, and FISA was adopted after it to limit domestic surveillance using the foreign intelligence excuse, which largely reduced the then-building pressure on the Court to resolve that issue. The loosening of FISA under the FISA Amendments Act and the subsequent mass surveillance means that the pressure is likely to return.

I wouldn't say US v. US District Court is a dead letter now. I would say that we are reaching the point where how the Supreme Court decides the issue it deferred then will determine whether it becomes a dead letter.