I don't think growing staples within cities will be economically viable within our lifetimes. As a general rule, agricultural land use orders itself around it's

I don't think growing staples within cities will be economically viable within our lifetimes. As a general rule, agricultural land use orders itself around it's markets according to transportation. The more delicate the produce, the closer the producers must be to a city. There's even a (very simple, it's from the 19th century) model for this, which is the Von Thünen's model of land use. I wish I had some actual data easy at hand to show you, but this is more or less observable from history. Until active refrigeration, spoilage losses associated with the more delicate agricultural products pretty much put them outside of the reach of the majority of urban dwellers. If you wanted any sort of fresh dairy, fresh meat, fresh vegetables or fresh fruit in say, the early 19th century, you'd better live on a farm. So whereas a farmer might have had fresh milk, a city worker would have cheese, and instead of fresh meat, cured meat, and so on. But anyway, in short of the whole world becoming one huge city, it's unlikely that staples would ever be grown inside them.