I agree in principle but I certainly don't think a national health care response to a pandemic should be based on it, as it is very challenging to fully identify all the members of vulnerable populations in a society. What reinfection cases would also indicate is the 'herd immunity' strategy promoted by the Declaration may no longer be a plausible approach to addressing the virus.
It's not super hard to identify at-risk populations now; we do it for RSV, flu, immunocompromised. It's not trying to invent something new.
Less related is the fact that the Declaration incorrectly asserts that governments prefer to do extended full lockdowns as a primary measure to curb the virus until a vaccine is created.
Lockdowns are what the governments want to do (with masks and SD); or at least, what they are doing/did. At least it's what is going on in NC from our governor, whose multi-phased plans are economically crippling and non-sensical.