I am pretty sure that Congress could do so a thing. Just because it ACTS like an Article III court doesn't mean it is one and since Congress created the whole thing, they can also change the whole thing.
Appellant invokes the principles of judicial independence and separation of powers that underlie article III, [citations omitted], but those principles are not implicated by appellant's speculation that a judge designated to the FISA court might be influenced by the possibility that his temporary assignment might be revoked. By statute, federal judges may be designated by the Chief Justice to serve temporarily on other courts, 28 U.S.C. §§ 291-296 (1982), and temporary designation within the federal judicial system has never been thought to undermine the judicial independence that article III was intended to secure.
A judge's appointment to the FISA court can be revoked (I emphasized this part above; the revocation, of course, can be enacted by Congress), but the judge still has a job for life - in the District Court.
The fact that FISA judges are article III judges does not make FISA an article III court. It is a court created by Congress, which is staffed by people who are already Article III judges. Cavanagh's attack on the independence of FISA judges is rooted in the fact that the assignment can be revoked.
Are you sure that's what that means? Reading the cases that decision cites in the "unbroken line" of failed separation of powers claims against FISA, nothing I've read unequivocally states that FISC is an Article III court, which makes sense to me because FISC is more unlike a federal court than like one.
