FACT: As currently interpreted, it is terrible public policy.
The court should latch onto the ambiguity of the text [A pox on ANYONE who claims that birthright citizenship is "in the Constitution." It is NOT], and reinterpret it to good public policy as follows: The text should highlight the word, "…reside.." at the end and state that illegals in the country do not RESIDE in the country in any meaningful way.
But they won't do that, and the only real speculation is how they will worm their way out of doing the right thing. They will NOT say that a Constitutional Amendment is required to correct the error, but they could throw it back to Congress to clarify by law.