"Refuse treatment" is too open to debate. Particularly legal debate.

What does it mean? WHEN do you refuse treatment? In what circumstances? and does it take into account that you may have signed the card ten years ago, when possible treatments have WAY surpassed what was possible when you made the decision?

This is a legal minefield. I do not think they will catch on. PARTICULARLY after a few court cases have shown them to be unworkable in practice.