There is also the equal protection angle. Obama has extended waivers to some Americans and not to others. The law does not apply equally. I don’t know why that hasn’t been brought up.
My take is that the Court could (but probably won't) find the law's uneven application a violation of the EP Clause. However, that would just change how the law should be applied. The Act itself would still be constitutional, at least in the eyes of Roberts' Court.
disclaimer - not a lawyer, never taken a law class.