Thats way to much of a stretch. Cause no ones gonna invest in new shopping carts for every store, and to make it too narrow for a cart to enter would be uncomfortably narrow for people.

and its unnecessary, just have maybe, depending on the size of the store, 2-4 self checkouts. and have a cashier on hand at all times to handle cart loads. 2 or more for high traffic hours. a lot simpler solution.