They are going to get the Apple ecosystem even more closed and make desktop consumer platform like iPhone. Steve Jobs' dream coming true. I have never seen Linux running great on a ARM consumer device (like android tablets, smartphones) except ChromeOS devices. The big issues being unavailable graphics and other drivers and lack of ACPI (devicetree has to be provided separately). Some attempts were able to get Linux on framebuffer with some X patches but system upgrades required special care and having just framebuffer is slow and useless. And that is what will be achievable at most. ARM means freedom for manufacturers, not for consumers/end users! I suspect Apple will also put there multiple proprietary accelerators and specialized chips to make things faster by offloading some work which won't be accessible from Linux, of course.