I assume the proposal is that the vaccine card would be a de-facto immunity card, where a test showing a high antibody count would still be logged on your card as an alternative to the vaccine.

But the devil's in the details anyways. How long would that be considered good for, since we'll probably be looking at regular annual boosters? Would extremist anti-vaxxers have a perverse incentive to get infected so as to rejoin society while avoiding the vaccine?