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.
Most famous merchant still not accepting bitcoin as payment including apple. But i do believe they will accept bitcoin in near future because cryptocurrency is future currency.
No say when and nobody can tell the exact date or year for acceptance of bitcoin by Apple. It is totally upto them. If we look other big companies that already accepted bitcoin as their payments, it seems that they will also accept bitcoin in the near future. World is gradually turning towards digital currency and it is sure that in the future the whole world will accept bitcoin.