For limited uses barcodes of all sorts can be used. 7-Eleven has a partnership with PayNearMe that lets people pay all sorts of bills (or even buy Greyhound bus tickets) using PayNearMe barcodes they just take to a nearby 7-Eleven. It can be printed or displayed on their phone.
And airlines are already using PDF417 2D barcodes on their boarding passes. People who check in online can print them out themselves.