Over the years, Apple has hired hundreds of semiconductor engineers to work on their chip designs and, under the late Steve Jobs’ guidance, crafted what one could call at least a 15-year plan to make the A series chips equal to or more powerful than the Intel processors they use today. I don’t think Apple has any plans to put their A series chips in a Mac soon.
But advancing the power and features of their A9 architecture and future processors goes well beyond their current device offerings. Rumors that Apple is working on a car is intriguing and, if true, it would need a powerful set of processors to handle the entertainment and navigations systems as well as any crash avoidance functions a smart car needs. I also see Apple eventually creating products for VR, AR, more advanced home automation, smarter TVs and perhaps even specialized gaming systems that would work with a future Apple TV system.
Although they could use chips from other vendors, advancing their own semiconductor architecture would give them more control of their designs and ecosystems.