Don't you mean two citizens as parents ( not natural born ). If it were natural born, then no descendants of immigrants ( and their descendants ) can ever be NBC.
Don't you mean two citizens as parents (not natural born). If it were natural born, then no descendants of immigrants (and their descendants) can ever be nbC.You are right that stated that way such a rule would be unworkable, but I suppose the intent was to define something else, to which I will give the label "hyper-natural born Citizen" (or hnbC) in order to distinguish it from the de Vattel nbC type.
A hyper-natural born Citizen (hnbC) is a citizen born in-country to parents who themselves were born in-country to parents who were citizens when the hnbC's parents were born.
A "hper-natural born Citizen" would go back an extra generation of citizenship purity over an ordinary natural born Citizen. While one might argue that this would add another protective generational layer of inbred allegiance and therefore make a beneficial requirement, this concept is almost exclusively a fabrication of those who are trying to further trivialize the founders' concept of nbC (which even large numbers of conservatives nowadays seem to have already rejected).
Those conflating this new hnbC concept with the historical version are almost all supporters of Ted Cruz who are disingenuously attempting to equate his birth bona-fides with Trump's in order to trivialize the very serious nature of Cruz's deficiency in this regard.
As far as I know, no one historically has ever advocated for the hnbC concept, but since it has been brought up here, I must state that I like it and think it would be good for the republic to require presidents to be hyper-natural born Citizens and for senators to be standard natural born Citizens (but that all is just silly fantasy at this point).