I suspect at some point they will simply drop Intel for their own (ARM) platform. I think moving will be easy once all app store submissions are in bitcode.
Towards the higher end, ARM can't hope to field anything in that timeline to compete with even todays i5 or i7s (or corresponding Xeons). Some people do use this kind of CPU power.
I don't think the switch would present a significant problem in marketing or for developers, so it would purely be a question of having the chips that fit the products. The Macbook, as you point out, is basically already there.