When they really need to. But they'll fight it hard! Apple's business model is to lock everything down -- very closed indeed. This does not align with the goals of bitcoin, at least, how I perceive them.
tl;dr Apple = closed. BTC = open.
I think they will soon accept bitcoin payments. If they recognize the potential of Bitcoin, they will surely have a bitcoin payment scheme. Because they are a technology company, they will easily know the potential of blockchain technology. Customers will be able to pay directly to Apple's wallet to own the phone.