I wonder if Apple is maybe looking at AMD for chips? That would be a much less painful switch instead of transitioning to ARM for the Desktop.
The got rid of the 3rd party ARM design in their iphones/ipads, going for their own ARM/AARCH64 design. They are currently in the process of getting rid of the PowerVR GPU, to be replaced with their own GPU.
Moving to their own AARCH64 CPU for laptops/desktops fits with that trend. Many people have been wondering 'when' this will happen, not if.
Moving to AMD doesn't fit with this long term trend.