It might be a little difficult for them if they are planning to implement this and claim to be 'reasonable' right after Xmas and the New Year since many people tend to buy lots of groceries at this time of year. However, I wouldn't be surprised, since when have they been reasonable and since they can plan events to scare and manipulate the way they want...
Also Feb/March would be 'enough' time after the festivities to claim that the Xmas shopping would be finished.
Alyscat - I agree that the panic shoppers would be an easiest to identify and perhaps thhose who buy with credit/debit cards?