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.
In my opinion, Apple is starting to lose its dominance in the tech industry. The last Iphone did not sell well because everyone knows that it's just the same from the last one with just a different name. I think we need Google, Facebook and Amazon to accept btc rather than a company that's going to die soon.