When I take the human aspect out of the Super Nations, yes I see your point.
Then I put it back in and realize that we wouldn't be resolving the dollar dictating care-- in some ways we would be complicating it and spreading it. It would get too big to understand, correct minor issues, and maintain. A World Health Care Plan would lend itself to the possibility of falling apart, being inadequate, and having a great impact on the largest scale.
Since health care is about ensuring people get what they need, I think we would have a hard time as Nations funding a health care plan knowing that part of what we are funding is benefiting another country. It would become a bargaining chip, another way nations can put pressure on each other in times of conflict.
The bottom line is, I don't think we would resolve the focus on cost because I don't think the Super Nations are competing with each other to have the best healthcare. I think nations are attempting to fulfill a necessity for their citizens and have little interest in the success of another nation's healthcare plans unless it is viewed as something to learn from and adopt something similar.
If we did develop a World Health Care Plan that actually worked better then the national systems in place, I don' think it would need to be on the global scale to be effective. Whatever that better model is, should be able to work on a smaller scale. I think the real issue is, what type of system is this? And, would this sustainable and effective health system actually have anything we would call "health care plans" at all?