Training teachers is probably the main physical cost (it was a big problem for computer science in France), but the main social obstacle is the opposition to change from basically everyone : parents don't want their children to learn different things than they did, teachers don't want to lose curriculum hours to make room for new subjects, and administrators don't want to risk making anything new.
It depends. Can you give some indication of what coalition with this intent you assume?
Additionally, I guess we assume that adequate monetary means are available for this endeavor, right? It is an investment, the new subject will start to pay off after 20 years earliest (30 if you have to teach the teachers), right?
Not sure whether setting this up as a related question that is hidden from the front page was the best approach. Maybe I should have selected that it should be posted to the front page instead. First time I'm using "Ask Related Question".
For instance, I imagine that if you introduced a new subject, it would be very expensive to make teachers be able to teach that subject. I suspect that to be the main constraint, but I'm not sure.