>In a realistic context, true multilingualism is very achievable, and not particularly exceptional throughout most of the world as many other commenters have pointed out. //
Implicitly you appear to suggest multilingualism is easy to achieve in [almost] all contexts?
Where parents are monolingual, and the pervading culture is monolingual then there's little opportunity for immersion and few people from whom to learn.
Yes. The core target audience of the article is likely unilingual families who will put their kid in French/Chinese/whatever classes to give them a leg up for Harvard admissions, 15 years later (or, in the NYTime's subtle language: "parents who want to give their kids a bilingual boost").
Obviously if the kid only speaks the language in the context of a classroom, true fluency will never be reached. In a realistic context, true multilingualism is very achievable, and not particularly exceptional throughout most of the world as many other commenters have pointed out.