The family of the anencephalic fetus ought to be commended for such a noble gesture. What a wonderful thought of wishing to donate a newborn's vital body organs to sick infants in dire need of transplants.
However, morally and ethically the parents could be doing humanity more of a disservice in the long run. It will be a lucky day for five or so other infants who need organ transplants. These babies will go forward leading healthy and normal lives. Theoretically humanity could suffer a loss of morality, in which medicine debates whether a person of intellect is more worthy of a life, that a person handicapped mentally is not worthy and maybe we could use these persons for transplants, also. We as human beings are not capable of knowing where to draw lines morally or ethically because we as humans have the ability to rationalize and make excuses. It's our nature to be this way.
It will be better in the long run if we just slam the door shut on this idea. We need to find some other way to help babies in need of transplants.