They introduced ARM to manage their fingerprint sensor and the TouchBar. Rumors had it that Apple is working on connecting the ARM chip to more subsystems so it can do background work like background refresh (or what that feature is called when the laptop is in sleep – PowerNap?). I see this as Apple slowly creating a hybrid (low energy ARM for easy tasks and faster x86 for speed). Maybe the goal is a complete transition to ARM and Apple starts to design their own MacBook (Pro) CPUs to gain more control (be less dependent on Intel’s varying release cycles).
I've been waiting for something like ever since I first got a Raspberry Pi.
Keep the x86 CPU around for active, high powered use, and then use a low power ARM CPU to run downloads and software updates while the PC is in an off or idle state.
They'll probably take a hybrid approach before going all-in. Use the ARM CPU for low-power, now-CPU requirements to avoid draining the battery. The ARM chips in the iPhone and iPad are very good, but they're not quad-core i7 good.
I could see that being a possibility in the future as the discussion moves away from firepower and more toward power consumption, which seems to be a focus of Apple products.