I don't want to undermine your basic point here -- I hope that you're right. Quinoa in particular might be a problem though, since it's already increasing in price due short supply. Mass adoption by America's schools would probably result in making it unsustainable both for the schools themselves and for South American communities that rely on it.
It doesn't look like quinoa can only be cultivated in particular regions, but rather that it takes time to get good crops going. The price should come down in a few years.
http://www.newser.com/story/114536/in-bolivia-a-quinoa-quand...