Anyone who has paid by smartphone at retail will recognize that it's not really ready for primetime. It's pretty surprising that retailers are using it at all considering how inefficient and time consuming it is compared to other payment methods.

Any solution that requires fidgeting with phone apps, internet connectivity, waiting for confirmations etc. is a non-starter for any mainstream retail environment. There's just no way it will be adopted until a workable alternative similar to existing payment methods comes along.