It actually seems a bit roundabout to me. He's proposing that Congress pass a rule of construction for the courts to interpret, in hopes that this will indirectly result in the offending statute being struck down or constrained. But a more direct route would be: propose repealing or amending the FISA authorizing statute.

That would also be more in line with Congress's constitutional duties. It's true that the courts should enforce a robust 4th amendment. But Congress does not need to force them to do so: it could simply not pass laws that violate the 4th amendment, or if it realizes it has done so, it can repeal those laws.

Actually, it isn't. Ambiguity in existing laws is exactly what has allowed the NSA to do what they've been doing.