In preference to credit and debit cards though? And is it a strong enough preference that retailers would make the investment in new transaction infrastructure? Especially when the vanguard of forward-thinking technology retailers have probably already invested in contactless recently?
That's the sort of question that Apple are probably mulling over, and unless their (unknown, possibly non-existent) proprietary, non-NFC solution is so good that it can confidently challenge those barriers, then they'd be wise to consider adopt existing technologies that have traction, like contactless. There are tens of millions of contactless credit and debit cards out there, tens of thousands of terminals in use (and I'm just talking about the UK), and they're working easily alongside legacy payment methods. Turning down that kind of deployment advantage would be a major opportunity cost of any alternative.
There were tens of millions of not-so-smart smartphones in the UK before the iPhone arrived; it counted for nothing.
If Apple decide to do mobile payments, it will transform them. They're never going to adopt existing technologies unless they can revolutionise them. In its current incarnation, NFC is not Apple-quality. If Apple use NFC, it will be an improved NFC that doesn't currently exist.