Well, I don't mind a system where you can donate your organs to someone specifically, but I don't like the idea of refusing organs to those who didn't opt in. I can see the 'fairness' of it, sure, but I also wouldn't want my medical system to refuse to pay for the medical care of those who refused to pay taxes, etc.
If you have universal coverage, you have universal coverage.
An 'opt out' system is so much better at getting organs anyway, that it's amazing. My region forces us to chose an opting when we get health insurance. There's no pressure for which choice to make, just that you have to make a choice. There's a large level of opt in, in such a system.