Two thoughts about this.
First - nobody who is entitled to US citizenship by descent from a US citizen parent NEEDS a CRBA. Because the CRBA aggregates other information, it's USEFUL to have one when you need a passport, or for other citizenship-related reasons, but it's not a requirement. Specifically, if there is not one, it does not mean Cruz is not or could not be a US citizen.
Second - if a child of mine was born abroad, I would be at the consulate THE VERY NEXT DAY to get his CRBA, understanding how important and how precious his American citizenship was, and also to demonstrate my resolve from his very first breath to raise him as an American AND NOTHING ELSE.
This second point, I think, is important to adjudicate whether or not any person born to an alien father in a foreign land could possibly meet the "natural born" requirement.
Remember, in 1970 Uncle Sam was still giving out involuntary scholarships to the University of Saigon, as any American living in Canada certainly knew. Regardless of the technicalities about Mama Cruz (did she register to vote in Canada, etc, etc) the failure to clarify - IMMEDIATELY - her and Señor Cruz's intentions about Little Ted's citizenship status does perhaps suggest some ambivalence - certainly (I was in college in 1970) the ability to assert Canadian citizenship was perceived at that time as quite valuable.
I doubt that any court will get involved in this matter unless the (very, very) unlikely circumstance of Ted Cruz's name being on 270+ electoral vote ballots on January 3, 2017 arises. But I do believe the failure to ask for a CRBA until 1986 raises legitimate questions about whether on not the intent of the Founders regarding NBC status would be met in this case.
-PJ