Hi serolf, Welcome to Cruise-Chat!
An alcohol card is actually available. It is limited to large group cruises and everyone in the group must buy into it. At least that is the way it used to work. They have a "Drink of the Day" card you can buy on board for $23 plus gratuities. It includes 5 drinks of the day (or your choice of them) and a souvenir glass with the first drink.
I sorta doubt they'll ever have an unlimited "booze" card available for general cruises though. They have been getting away from the reputation of being the party ships for many years now. You never know though, things change everyday.