Relative to x86, a lot more ARM use cases are in the embedded space, where one vendor writes all the software that will ever run on the CPU. So I think there's

Relative to x86, a lot more ARM use cases are in the embedded space, where one vendor writes all the software that will ever run on the CPU. So I think there's merit to the idea that it's easier for ARM to break backwards compatibility than Intel can. Of course, a lot of ARM use cases also don't have that luxury. Android apps using the NDK are the most obvious example. The Raspberry Pi is another example: the RPi3 is still on 32-bit, held there by binary blob drivers and the massive amount of effort needed to create the fully open source driver stack that's a prerequisite for moving over (Eric Anholt is doing an incredible job; it just takes time).