I see a very strong argument for Rubio being an NBC. But if one parent, and more so the father, is a foreigner it is clear what that child is not.
I'm a believer in original intent and understanding in construing the meaning of Constitutional text. I don't know what English common law (much of the framers' point of reference) was at the time regarding this and SCOTUS hasn't clarified it as far as I know.
I think the framers intentionally laid down broad legal standards within which future generations would resolve (NOT by CHANGING the constitution from the bench, but by APPLYING the original meaning to the issue of the day). Having said that, I'm inclined to think without deciding that if a child is native born to parents who obviously demonstrate their loyalty to the U.S. by subsequently becoming citizens nothing unpatriotic notwithstanding, the child should be considered a NBC. That's my gut feel, not the result of a diligent research which I hope would agree - but if it clearly did not, then as judge or Justice, I would have to rule the other way regardless of my personal views. If an honest and diligent inquiry came up with that it could go either way, then I think allowing Rubio to be an NBC would not be an unjust decision.