“judges are very conscious of their limitations”
Sorry. The US Supreme Court has no problem at all with creating law out of thin air. Think abortion, or the “right” to homosexuality...kind of hard to find THOSE in the US Constitution!
If Cruz ran, and one state put him on the ballot and another refused, you would have a valid federal case, just as Florida’s recount methods fell under the federal judiciary.
A court would not have to define natural born citizen or weigh the factual evidence regarding Cruz’s qualifications to determine that he should be permitted to appear on the ballot so that voters and their electors can determine his eligibility.