Quick question -- what's so good about ARM specifically? Aren't there other minimal architectures, maybe even one with lower/no licensing costs?
Longer: Intel has continually sucked at mobile (likely due to innovator's dilemma and it's love-hate relationship with Microsoft which also sucks at mobile), and this may mean a stronger shift by Apple to integration with it's priorities (security, iOS/WatchOS friendliness, better battery life).