Of course, if the nutritional value of day-to-day food is going to decrease, it is alarming.
But I think that, in some sense, it is rather a good thing: because, nowadays, people don't know how to be sustainable out of the system. For instance, in my country (France), we import all the rice (and many other things) we eat. In actual fact, this is nonsense, because nature is generous: everything is available for people who know what they are looking for. As an example, if you are looking for nutrients similar to the ones found in rice, you might try couch grass roots (Elymus Repens). With the starch contained in the roots of this plant, you can even make beer (just like with rice). So maybe, in the future, if rice is no longer available, people will start looking for food available in the place they are?