The GST is not proportional to income. Very poor people pay the same amount as very wealthy.
If multi-millionaires and even wealthier were forced to use a cashless card they could be charged a higher more proportionate amount of GST.
I also feel that many businesses would relish charging a millionaire $20 for a carton of milk.
I also feel that the super-rich would call in their corporate army to burn the place down if somebody tried to implement it(but that's just the cynic in me).
Just on the merit of whether GST should be proportionate to income, should the uber rich be on a higher rate of gst with a special shopping card?
(ps don't say this is just one of their fancy exclusive credit cards)