Unless Apple is making a car that will cost $10K and drive itself, this will be a niche product. Look at all the research that says people are moving more and more to high density cities. Those people are relying on mass transit. Those people look like.......current iPhone users. I'm a suburbanite, if the price is right (WHICH I DOUBT SINCERELY!!) I'll be interested in an Apple car, but the millenials that report to me? They don't own cars and the ones that do, regret buying them.
What's left, the developing world? Nope. They might want vehicles, but they don't have the infrastructue or wealth to support an Apple car.
China? Most of the country is still dirt poor. Yes, you have a HUGE middle class, but they too are in high density cities and rely on mass transit.
Apple needs to do something revolutionary with regards to the phone and the tablet. They need to push all the goodies they have in the labs that they're trying to meter out to us. They need to skip the iPhone 8 and go straigh to the 10.
Face it, they're facing seriously diminishing returns. Look at the growth of that R&D trend. What have all those billions bought them? Apple pencil? IPad pro? All great, but not reveloutionary and nothing that will make folks say an imphatic NO! To Samsung and Microsoft.
Apple needs to do something to completely change the conversation. The iPhone made everyone completely rethink how they thought about phones. That said, Android isn't sitting still. They want their billions also. The Galaxy Note 5 is sooo much better than the iPhone. I can't live without my iPad, but I do skip a generation.
Apple is facing what all mega profitable corporations face, the unbreakable law of large numbers. Good luck to them.