As Lance Whitney wrote in his piece, "What Apple needs to offer with the iPhone 6," rumors that Apple would adopt NFC (near-field communications) -- most often talked about in connection with mobile payments, but potentially useful for other things -- have bounced around the past couple of years. But the technology is still a no-show.
A lot of companies have been dabbling with NFC, and several rival smartphones support it. However, NFC has a way to go before it reaches critical mass. Apple is likely waiting for that to happen before it adds it to the iPhone.
However, it's worth noting that in a 2012 interview, Apple Senior Vice President Phil Schiller said that it isn't clear that NFC is a solution to any current problem. "Passbook does the kinds of things customers need today," he said. So it's also possible Apple may never bring NFC to its mobile devices and continue developing its own mobile payments solution, which could be combined with the new fingerprint sensor integrated into the home button on the 5S.