True, but it still makes it more difficult since there really can't be an official system for proving vaccination, and we already know the vaccination cards are very open to fraud. A system like this could work in some places, as long as the vaccinated people where given some sort of easily seen wrist band to prove they are allowed to remove their masks, but it would still make enforcement more difficult.
Might be worth while for a theme park to do, but I can't see most businesses wanting to bother with this.