The million dollar question is at what exchange rate...and why? What items are priced in dollars except real estate (which nobody wants en blanco)? The merchant has everything priced in pesos, why would anyone use their dollars to buy bread?
Ironically, getting rid of the cepo and forcefully closing any brecha through devaluation makes the USD useless in domestic commerce. The only benefit I could see would be merchants offering discounts on USD purchases so that they can later pay foreign suppliers in USD without having to wait in line for requests to the government for import currency. This would probably only benefit the wholesale sector anyway, not your local store.
Why doesn't the government just get rid of the Dolar Turista while we are at it, since this is the actual benefit of a USD debit card. Oh wait, we can't have that...