If they follow existing precedent, it looks like ...
The alternative is SCOTUS give Congress the power to define natural born citizen via Act of Congress. All the act need do is attach citizenship at birth. It could do that for the whole world, literally, and be constitutional, if SCOTUS finds the power to lie with Congress.
IRREFUTABLE AUTHORITY HAS SPOKEN
(Oct. 18, 2009) The Post & Email has in several articles mentioned that the Supreme Court of the United States has given the definition of what a ‘natural born citizen’ is. Since being a natural born citizen is an objective qualification and requirement of office for the U.S. President (and VP), it is important for all U.S. Citizens to understand what this term means.
http://www.thepostemail.com/2009/10/18/4-supreme-court-cases-define-natural-born-citizen/
"But it [the first sentence of the Fourteenth Amendment] has not touched the acquisition of citizenship by being born abroad of American parents; and has left that subject to be regulated, as it had always been, by Congress, in the exercise of the power conferred by the Constitution to establish an uniform rule of naturalization."In establishing a uniform rule of naturalization, Congress defines who requires naturalization and who does not because (s)he is already a citizen at birth.In doing so the Court said in Rogers v. Bellei:
Thus, at long last, there emerged an express constitutional definition of citizenship. But it was one restricted to the combination of three factors, each and all significant: birth in the United States, naturalization in the United States, and subjection to the jurisdiction of the United States. The definition obviously did not apply to any acquisition of citizenship by being born abroad of an American parent. That type, and any other not covered by the Fourteenth Amendment, was necessarily left to proper congressional action.
The Court has recognized the existence of this power. It has observed, "No alien has the slightest right to naturalization unless all statutory requirements are complied with . . . ." (snip) And the Court has specifically recognized the power of Congress not to grant a United States citizen the right to transmit citizenship by descent.
And, surely, you believe that a country has an inherent right - as SCOTUS has said many times - to say who are its citizens?