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.
Bitcoin don't need to adapt to the world but the world need to adapt to bitcoin. When bitcoin is adopted by most of people then apple should accept bitcoin if not then apple will have a problem on it's business. I prefer like to see google and YouTube to accept bitcoin. Apple don't have to accept bitcoin but I think it will be better if it accept bitcoin for it's better future.